[FFmpeg-devel,1/2] Provided support for MPEG-5 EVC (Essential Video Coding) codec

- Added new entry to codec IDs list
- Added new entry to the codec descriptor list
- Bumped libavcodec minor version
- Changes in Changelog and MAINTAINERS files
- Added xeve encoder wrapper
- Added xevd dencoder wrapper
- Added documentation for xeve and xevd wrappers
- Added parser for EVC format
- Changes in project configuration file and libavcodec Makefile

Signed-off-by: Dawid Kozinski <d.kozinski@samsung.com>
---
 Changelog                 |   3 +-
 MAINTAINERS               |   2 +
 configure                 |   8 +
 doc/decoders.texi         |  24 ++
 doc/encoders.texi         |  92 ++++++
 doc/general_contents.texi |  19 ++
 libavcodec/Makefile       |   3 +
 libavcodec/allcodecs.c    |   2 +
 libavcodec/avcodec.h      |   3 +
 libavcodec/codec_desc.c   |   8 +
 libavcodec/codec_id.h     |   1 +
 libavcodec/evc_parser.c   | 526 +++++++++++++++++++++++++++++++++
 libavcodec/libxevd.c      | 436 ++++++++++++++++++++++++++++
 libavcodec/libxeve.c      | 597 ++++++++++++++++++++++++++++++++++++++
 libavcodec/parsers.c      |   1 +
 libavcodec/profiles.c     |   6 +
 libavcodec/profiles.h     |   1 +
 libavcodec/version.h      |   2 +-
 18 files changed, 1732 insertions(+), 2 deletions(-)
 create mode 100644 libavcodec/evc_parser.c
 create mode 100644 libavcodec/libxevd.c
 create mode 100644 libavcodec/libxeve.c

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/evc_parser.c b/libavcodec/evc_parser.c
> new file mode 100644
> index 0000000000..b2136a6b45
> --- /dev/null
> +++ b/libavcodec/evc_parser.c
> @@ -0,0 +1,526 @@
> +/*
> + * EVC format parser
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <stdint.h>
> +
> +#include "libavutil/common.h"
> +
> +#include "parser.h"
> +#include "golomb.h"
> +
> +// The length field that indicates the length in bytes of the following NAL unit is configured to be of 4 bytes
> +#define EVC_NAL_UNIT_LENGTH_BYTE        (4)  /* byte */
> +
> +#define EVC_NAL_HEADER_SIZE             (2)  /* byte */
> +#define MAX_SPS_CNT                     (16) /* defined value in EVC standard */
> +
> +// NALU types
> +// @see ISO_IEC_23094-1_2020 7.4.2.2 NAL unit header semantics
> +//
> +#define EVC_NUT_NONIDR                  (0)  /* Coded slice of a non-IDR picture */
> +#define EVC_NUT_IDR                     (1)  /* Coded slice of an IDR picture */
> +#define EVC_NUT_SPS                     (24) /* Sequence parameter set */
> +#define EVC_NUT_PPS                     (25) /* Picture paremeter set */
> +#define EVC_NUT_APS                     (26) /* Adaptation parameter set */
> +#define EVC_NUT_FD                      (27) /* Filler data */
> +#define EVC_NUT_SEI                     (28) /* Supplemental enhancement information */
> +
> +// The sturcture reflects SPS RBSP(raw byte sequence payload) layout
> +// @see ISO_IEC_23094-1 section 7.3.2.1
> +//
> +// The following descriptors specify the parsing process of each element
> +// u(n) - unsigned integer using n bits
> +// ue(v) - unsigned integer 0-th order Exp_Golomb-coded syntax element with the left bit first
> +typedef struct EVCParserSPS {
> +    int sps_seq_parameter_set_id;   // ue(v)
> +    int profile_idc;                // u(8)
> +    int level_idc;                  // u(8)
> +    int toolset_idc_h;              // u(32)
> +    int toolset_idc_l;              // u(32)
> +    int chroma_format_idc;          // ue(v)
> +    int pic_width_in_luma_samples;  // ue(v)
> +    int pic_height_in_luma_samples; // ue(v)
> +    int bit_depth_luma_minus8;      // ue(v)
> +    int bit_depth_chroma_minus8;    // ue(v)
> +
> +    int sps_btt_flag;                           // u(1)
> +    int log2_ctu_size_minus5;                   // ue(v)
> +    int log2_min_cb_size_minus2;                // ue(v)
> +    int log2_diff_ctu_max_14_cb_size;           // ue(v)
> +    int log2_diff_ctu_max_tt_cb_size;           // ue(v)
> +    int log2_diff_min_cb_min_tt_cb_size_minus2; // ue(v)
> +
> +    int sps_suco_flag;                       // u(1)
> +    int log2_diff_ctu_size_max_suco_cb_size; // ue(v)
> +    int log2_diff_max_suco_min_suco_cb_size; // ue(v)
> +
> +    int sps_admvp_flag;     // u(1)
> +    int sps_affine_flag;    // u(1)
> +    int sps_amvr_flag;      // u(1)
> +    int sps_dmvr_flag;      // u(1)
> +    int sps_mmvd_flag;      // u(1)
> +    int sps_hmvp_flag;      // u(1)
> +
> +    int sps_eipd_flag;                 // u(1)
> +    int sps_ibc_flag;                  // u(1)
> +    int log2_max_ibc_cand_size_minus2; // ue(v)
> +
> +    int sps_cm_init_flag; // u(1)
> +    int sps_adcc_flag;    // u(1)
> +
> +    int sps_iqt_flag; // u(1)
> +    int sps_ats_flag; // u(1)
> +
> +    int sps_addb_flag;   // u(1)
> +    int sps_alf_flag;    // u(1)
> +    int sps_htdf_flag;   // u(1)
> +    int sps_rpl_flag;    // u(1)
> +    int sps_pocs_flag;   // u(1)
> +    int sps_dquant_flag; // u(1)
> +    int sps_dra_flag;    // u(1)
> +
> +    int log2_max_pic_order_cnt_lsb_minus4; // ue(v)
> +    int log2_sub_gop_length;               // ue(v)
> +    int log2_ref_pic_gap_length;           // ue(v)
> +
> +    int max_num_tid0_ref_pics; // ue(v)
> +
> +    int sps_max_dec_pic_buffering_minus1; // ue(v)
> +    int long_term_ref_pic_flag;           // u(1)
> +    int rpl1_same_as_rpl0_flag;           // u(1)
> +    int num_ref_pic_list_in_sps[2];       // ue(v)
> +
> +    int picture_cropping_flag;      // u(1)
> +    int picture_crop_left_offset;   // ue(v)
> +    int picture_crop_right_offset;  // ue(v)
> +    int picture_crop_top_offset;    // ue(v)
> +    int picture_crop_bottom_offset; // ue(v)
> +
> +} EVCParserSPS;
> +
> +typedef struct EVCParserContext {
> +    ParseContext pc;
> +    EVCParserSPS sps[MAX_SPS_CNT];
> +    int is_avc;
> +    int nal_length_size;
> +    int to_read;
> +    int incomplete_nalu_prefix_read; // The flag is set to 1 when an incomplete NAL unit prefix has been read
> +
> +    int got_sps;
> +    int got_pps;
> +    int got_sei;
> +    int got_slice;
> +} EVCParserContext;
> +
> +static int get_nalu_type(const uint8_t *bits, int bits_size, AVCodecContext *avctx)
> +{
> +    int unit_type_plus1 = 0;
> +
> +    if(bits_size >= EVC_NAL_HEADER_SIZE) {
> +        unsigned char *p = (unsigned char *)bits;
> +        // forbidden_zero_bit
> +        if ((p[0] & 0x80) != 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information. Malformed bitstream.\n");
> +            return -1;
> +        }
> +
> +        // nal_unit_type
> +        unit_type_plus1 = (p[0] >> 1) & 0x3F;
> +    }
> +
> +    return unit_type_plus1 - 1;
> +}
> +
> +static uint32_t read_nal_unit_length(const uint8_t *bits, int bits_size, AVCodecContext *avctx)
> +{
> +    uint32_t nalu_len = 0;
> +
> +    if(bits_size >= EVC_NAL_UNIT_LENGTH_BYTE) {
> +
> +        int t = 0;
> +        unsigned char *p = (unsigned char *)bits;
> +
> +        for(int i = 0; i < EVC_NAL_UNIT_LENGTH_BYTE; i++)
> +            t = (t << 8) | p[i];
> +
> +        nalu_len = t;
> +        if(nalu_len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size!\n");
> +            return 0;
> +        }
> +    }
> +
> +    return nalu_len;
> +}
> +
> +// @see ISO_IEC_23094-1 (7.3.2.1 SPS RBSP syntax)
> +static EVCParserSPS *parse_sps(const uint8_t *bs, int bs_size, EVCParserContext *ev)
> +{
> +    GetBitContext gb;
> +    EVCParserSPS *sps;
> +    int sps_seq_parameter_set_id;
> +
> +    if(init_get_bits8(&gb, bs, bs_size) < 0)
> +        return NULL;
> +
> +    sps_seq_parameter_set_id = get_ue_golomb(&gb);
> +
> +    if(sps_seq_parameter_set_id >= MAX_SPS_CNT)
> +        return NULL;
> +
> +    sps = &ev->sps[sps_seq_parameter_set_id];
> +    sps->sps_seq_parameter_set_id = sps_seq_parameter_set_id;
> +
> +    // the Baseline profile is indicated by profile_idc eqal to 0
> +    // the Main profile is indicated by profile_idc eqal to 1
> +    sps->profile_idc = get_bits(&gb, 8);
> +
> +    sps->level_idc = get_bits(&gb, 8);
> +
> +    skip_bits_long(&gb, 32); /* skip toolset_idc_h */
> +    skip_bits_long(&gb, 32); /* skip toolset_idc_l */
> +
> +    // 0 - monochrome
> +    // 1 - 4:2:0
> +    // 2 - 4:2:2
> +    // 3 - 4:4:4
> +    sps->chroma_format_idc = get_ue_golomb(&gb);
> +
> +    sps->pic_width_in_luma_samples = get_ue_golomb(&gb);
> +    sps->pic_height_in_luma_samples = get_ue_golomb(&gb);
> +
> +    sps->bit_depth_luma_minus8 = get_ue_golomb(&gb);
> +    sps->bit_depth_chroma_minus8 = get_ue_golomb(&gb);
> +
> +    sps->sps_btt_flag = get_bits(&gb, 1);
> +    if(sps->sps_btt_flag) {
> +        sps->log2_ctu_size_minus5 = get_ue_golomb(&gb);
> +        sps->log2_min_cb_size_minus2 = get_ue_golomb(&gb);
> +        sps->log2_diff_ctu_max_14_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_ctu_max_tt_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_min_cb_min_tt_cb_size_minus2 = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_suco_flag = get_bits(&gb, 1);
> +    if(sps->sps_suco_flag) {
> +        sps->log2_diff_ctu_size_max_suco_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_max_suco_min_suco_cb_size = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_admvp_flag = get_bits(&gb, 1);
> +    if(sps->sps_admvp_flag) {
> +        sps->sps_affine_flag = get_bits(&gb, 1);
> +        sps->sps_amvr_flag = get_bits(&gb, 1);
> +        sps->sps_dmvr_flag = get_bits(&gb, 1);
> +        sps->sps_mmvd_flag = get_bits(&gb, 1);
> +        sps->sps_hmvp_flag = get_bits(&gb, 1);
> +    }
> +
> +    sps->sps_eipd_flag =  get_bits(&gb, 1);
> +    if(sps->sps_eipd_flag) {
> +        sps->sps_ibc_flag = get_bits(&gb, 1);
> +        if(sps->sps_ibc_flag)
> +            sps->log2_max_ibc_cand_size_minus2 = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_cm_init_flag = get_bits(&gb, 1);
> +    if(sps->sps_cm_init_flag)
> +        sps->sps_adcc_flag = get_bits(&gb, 1);
> +
> +    sps->sps_iqt_flag = get_bits(&gb, 1);
> +    if(sps->sps_iqt_flag)
> +        sps->sps_ats_flag = get_bits(&gb, 1);
> +
> +    sps->sps_addb_flag = get_bits(&gb, 1);
> +    sps->sps_alf_flag = get_bits(&gb, 1);
> +    sps->sps_htdf_flag = get_bits(&gb, 1);
> +    sps->sps_rpl_flag = get_bits(&gb, 1);
> +    sps->sps_pocs_flag = get_bits(&gb, 1);
> +    sps->sps_dquant_flag = get_bits(&gb, 1);
> +    sps->sps_dra_flag = get_bits(&gb, 1);
> +
> +    if(sps->sps_pocs_flag)
> +        sps->log2_max_pic_order_cnt_lsb_minus4 = get_ue_golomb(&gb);
> +
> +    if(!sps->sps_pocs_flag || !sps->sps_rpl_flag) {
> +        sps->log2_sub_gop_length = get_ue_golomb(&gb);
> +        if(sps->log2_sub_gop_length == 0)
> +            sps->log2_ref_pic_gap_length = get_ue_golomb(&gb);
> +    }
> +
> +    return sps;
> +}
> +
> +static int parse_nal_units(AVCodecParserContext *s, const uint8_t *bs,
> +                           int bs_size, AVCodecContext *avctx)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +    int nalu_type, nalu_size;
> +    unsigned char *bits = (unsigned char *)bs;
> +    int bits_size = bs_size;
> +
> +    avctx->codec_id = AV_CODEC_ID_EVC;
> +
> +    nalu_size = read_nal_unit_length(bits, bits_size, avctx);
> +    if(nalu_size == 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit size: (%d)\n", nalu_size);
> +        return -1;
> +    }
> +
> +    bits += EVC_NAL_UNIT_LENGTH_BYTE;
> +    bits_size -= EVC_NAL_UNIT_LENGTH_BYTE;
> +
> +    nalu_type = get_nalu_type(bits, bits_size, avctx);
> +
> +    bits += EVC_NAL_HEADER_SIZE;
> +    bits_size -= EVC_NAL_HEADER_SIZE;
> +
> +    if (nalu_type == EVC_NUT_SPS) { // NAL Unit type: SPS (Sequence Parameter Set)
> +        EVCParserSPS *sps;
> +
> +        sps = parse_sps(bits, bits_size, ev);
> +
> +        avctx->coded_width         = sps->pic_width_in_luma_samples;
> +        avctx->coded_height        = sps->pic_height_in_luma_samples;
> +        avctx->width               = sps->pic_width_in_luma_samples;
> +        avctx->height              = sps->pic_height_in_luma_samples;

These should be set in the AVCodecParserContext, not the AVCodecContext.

> +
> +        if(sps->profile_idc == 0) avctx->profile = FF_PROFILE_EVC_BASELINE;
> +        else if (sps->profile_idc == 1) avctx->profile = FF_PROFILE_EVC_MAIN;

Setting these two is ok.

> +        else {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported profile (%d)\n", sps->profile_idc);
> +            return -1;

Do you really need to abort here? Not recognizing the profile can't 
possibly mean the bitstream can't be parsed further to fetch other 
information.

> +        }
> +
> +        // Currently XEVD decoder supports ony YCBCR420_10LE chroma format for EVC stream
> +        switch(sps->chroma_format_idc) {
> +        case 0: /* YCBCR400_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR400_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +            return -1;
> +        case 1: /* YCBCR420_10LE */
> +            avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +            break;
> +        case 2: /* YCBCR422_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR422_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +            return -1;
> +        case 3: /* YCBCR444_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR444_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +            return -1;
> +        default:
> +            avctx->pix_fmt = AV_PIX_FMT_NONE;

Fill s->format instead of avctx->pix_fmt.

> +            av_log(avctx, AV_LOG_ERROR, "Unknown supported chroma format\n");
> +            return -1;
> +        }
> +
> +        // The current implementation of parse_sps function doesn't handle VUI parameters parsing,
> +        // so at the moment it's impossible to initialize has_b_frames and max_b_frames AVCodecContex fields here.
> +        // Currently, initialization of has_b_frames and max_b_frames AVCodecContex fields have been moved to
> +        // libxevd_decode function where we can use xevd_config function being a part of xevd library API
> +        // to get the needed information.
> +        // However, if it will be needed, parse_sps function should be extended to handle VUI parameters parsing
> +        // and the following lines should be used to initialize has_b_frames and max_b_frames fields of the AVCodecContex.

There's no need no fill any of those field in this parser. What you can 
fill is avctx->color{space,_primaries,_trc,_range}, so mention that to 
add VUI parsing at some point.

> +        //
> +        // sps->vui_parameters.num_reorder_pics
> +        // if (sps->bitstream_restriction_flag && sps->vui_parameters.num_reorder_pics) {
> +        //     avctx->has_b_frames = sps->vui_parameters.num_reorder_pics;
> +        // }
> +
> +        ev->got_sps = 1;
> +
> +    } else if (nalu_type == EVC_NUT_PPS) // NAL Unit type: PPS (Video Parameter Set)
> +        ev->got_pps = 1;
> +    else if(nalu_type == EVC_NUT_SEI) // NAL unit type: SEI (Supplemental Enhancement Information)
> +        ev->got_sei = 1;

These got_* variables seem to be write only.

> +    else if (nalu_type == EVC_NUT_IDR || nalu_type == EVC_NUT_NONIDR) // NAL Unit type: Coded slice of a IDR or non-IDR picture

In here you should parse enough data to get the picture type (I, P, B) 
and set s->pict_type, and based on (i suppose) nalu_type, also set 
s->key_frame to 1 or 0.
At the start of this function, you'd ideally set them to 
AV_PICTURE_TYPE_NONE and -1 respectively, as "safe" defaults.

s->picture_structure should also be always set to 
AV_PICTURE_STRUCTURE_FRAME, as i assume this codec does not support 
interlacing.

> +        ev->got_slice++;
> +    else {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit type: %d\n", nalu_type);
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +/**
> + * Find the end of the current frame in the bitstream.
> + * @return the position of the first byte of the next frame, or END_NOT_FOUND
> + */
> +static int evc_find_frame_end(AVCodecParserContext *s, const uint8_t *buf,
> +                              int buf_size, AVCodecContext *avctx)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +
> +    if(!ev->to_read) {
> +        int nal_unit_size = 0;
> +        int next = END_NOT_FOUND;
> +
> +        // This is the case when buffer size is not enough for buffer to store NAL unit length
> +        if(buf_size < EVC_NAL_UNIT_LENGTH_BYTE) {
> +            ev->to_read = EVC_NAL_UNIT_LENGTH_BYTE;
> +            ev->nal_length_size = buf_size;
> +            ev->incomplete_nalu_prefix_read  = 1;
> +
> +            return END_NOT_FOUND;
> +        }
> +
> +        nal_unit_size = read_nal_unit_length(buf, buf_size, avctx);
> +        ev->nal_length_size = EVC_NAL_UNIT_LENGTH_BYTE;
> +
> +        next = nal_unit_size + EVC_NAL_UNIT_LENGTH_BYTE;
> +        ev->to_read = next;
> +        if(next < buf_size)
> +            return next;
> +        else
> +            return END_NOT_FOUND;
> +    } else if(ev->to_read > buf_size)
> +        return END_NOT_FOUND;
> +    else {
> +        if(ev->incomplete_nalu_prefix_read  == 1) {
> +            EVCParserContext *ev = s->priv_data;
> +            ParseContext *pc = &ev->pc;
> +            uint8_t nalu_len[EVC_NAL_UNIT_LENGTH_BYTE] = {0};
> +            int nal_unit_size = 0;
> +
> +            // 1. pc->buffer contains previously read bytes of NALU prefix
> +            // 2. buf contains the rest of NAL unit prefix bytes
> +            //
> +            // ~~~~~~~
> +            // EXAMPLE
> +            // ~~~~~~~
> +            //
> +            // In the following example we assumed that the number of already read NAL Unit prefix bytes is equal 1
> +            //
> +            // ----------
> +            // pc->buffer -> conatins already read bytes
> +            // ----------
> +            //              __ pc->index == 1
> +            //             |
> +            //             V
> +            // -------------------------------------------------------
> +            // |   0   |   1   |   2   |   3   |   4   | ... |   N   |
> +            // -------------------------------------------------------
> +            // |  0x00 |  0xXX |  0xXX |  0xXX |  0xXX | ... |  0xXX |
> +            // -------------------------------------------------------
> +            //
> +            // ----------
> +            // buf -> contains newly read bytes
> +            // ----------
> +            // -------------------------------------------------------
> +            // |   0   |   1   |   2   |   3   |   4   | ... |   N   |
> +            // -------------------------------------------------------
> +            // |  0x00 |  0x00 |  0x3C |  0xXX |  0xXX | ... |  0xXX |
> +            // -------------------------------------------------------
> +            //
> +            for(int i = 0; i < EVC_NAL_UNIT_LENGTH_BYTE; i++) {
> +                if(i < pc->index)
> +                    nalu_len[i] = pc->buffer[i];
> +                else
> +                    nalu_len[i] = buf[i - pc->index];
> +            }
> +
> +            // ----------
> +            // nalu_len
> +            // ----------
> +            // ---------------------------------
> +            // |   0   |   1   |   2   |   3   |
> +            // ---------------------------------
> +            // |  0x00 |  0x00 |  0x00 |  0x3C |
> +            // ---------------------------------
> +            // | NALU LENGTH                   |
> +            // ---------------------------------
> +            // NAL Unit lenght =  60 (0x0000003C)
> +
> +            nal_unit_size = read_nal_unit_length(nalu_len, EVC_NAL_UNIT_LENGTH_BYTE, avctx);
> +
> +            ev->to_read = nal_unit_size + EVC_NAL_UNIT_LENGTH_BYTE - pc->index;
> +
> +            ev->incomplete_nalu_prefix_read = 0;
> +
> +            if(ev->to_read > buf_size)
> +                return END_NOT_FOUND;
> +            else
> +                return ev->to_read;
> +        }
> +        return ev->to_read;
> +    }
> +
> +    return END_NOT_FOUND;
> +}
> +
> +static int evc_parser_init(AVCodecParserContext *s)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +
> +    ev->got_sps = 0;
> +    ev->got_pps = 0;
> +    ev->got_sei = 0;
> +    ev->got_slice = 0;
> +    ev->nal_length_size = EVC_NAL_UNIT_LENGTH_BYTE;
> +    ev->incomplete_nalu_prefix_read = 0;
> +
> +    return 0;
> +}
> +
> +static int evc_parse(AVCodecParserContext *s, AVCodecContext *avctx,
> +                     const uint8_t **poutbuf, int *poutbuf_size,
> +                     const uint8_t *buf, int buf_size)
> +{
> +    int next;
> +    EVCParserContext *ev = s->priv_data;
> +    ParseContext *pc = &ev->pc;
> +    int is_dummy_buf = !buf_size;
> +    const uint8_t *dummy_buf = buf;
> +
> +    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES)
> +        next = buf_size;
> +    else {
> +        next = evc_find_frame_end(s, buf, buf_size, avctx);
> +        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
> +            *poutbuf      = NULL;
> +            *poutbuf_size = 0;
> +            ev->to_read -= buf_size;
> +            return buf_size;
> +        }
> +    }
> +
> +    is_dummy_buf &= (dummy_buf == buf);
> +
> +    if (!is_dummy_buf)
> +        parse_nal_units(s, buf, buf_size, avctx);
> +
> +    *poutbuf      = buf;
> +    *poutbuf_size = buf_size;
> +    ev->to_read -= next;
> +
> +    return next;
> +}
> +
> +const AVCodecParser ff_evc_parser = {
> +    .codec_ids      = { AV_CODEC_ID_EVC },
> +    .priv_data_size = sizeof(EVCParserContext),
> +    .parser_init    = evc_parser_init,
> +    .parser_parse   = evc_parse,
> +    .parser_close   = ff_parse_close,
> +};

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/libxevd.c b/libavcodec/libxevd.c
> new file mode 100644
> index 0000000000..8ba2d89cbd
> --- /dev/null
> +++ b/libavcodec/libxevd.c
> @@ -0,0 +1,436 @@
> +/*
> + * libxevd decoder
> + * EVC (MPEG-5 Essential Video Coding) decoding using XEVD MPEG-5 EVC decoder library
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <float.h>
> +#include <stdlib.h>
> +
> +#include <xevd.h>
> +
> +#include "libavutil/internal.h"
> +#include "libavutil/common.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/pixdesc.h"
> +#include "libavutil/pixfmt.h"
> +#include "libavutil/imgutils.h"
> +#include "libavutil/cpu.h"
> +
> +#include "avcodec.h"
> +#include "internal.h"
> +#include "packet_internal.h"
> +#include "codec_internal.h"
> +
> +#define XEVD_PARAM_BAD_NAME -1
> +#define XEVD_PARAM_BAD_VALUE -2
> +
> +#define EVC_NAL_HEADER_SIZE 2 /* byte */
> +
> +/**
> + * The structure stores all the states associated with the instance of Xeve MPEG-5 EVC decoder
> + */
> +typedef struct XevdContext {
> +    const AVClass *class;
> +
> +    XEVD id;            // XEVD instance identifier @see xevd.h
> +    XEVD_CDSC cdsc;     // decoding parameters @see xevd.h
> +
> +    int decod_frames;   // number of decoded frames
> +    int packet_count;   // number of packets created by decoder
> +} XevdContext;
> +
> +/**
> + * The function returns a pointer to a variable of type XEVD_CDSC.

This doesn't seem to be the case.

> + * XEVD_CDSC contains all decoder parameters that should be initialized before its use.
> + *
> + * The field values of the XEVD_CDSC structure are populated based on:
> + * - the corresponding field values of the AvCodecConetxt structure,
> + * - the xevd decoder specific option values,
> + *   (the full list of options available for the xevd encoder is displayed after executing the command ./ffmpeg --help decoder = libxevd)
> + * - and the xevd encoder options specified as a list of key-value pairs following the xevd-params option
> + *
> + * Order of input processing and populating the XEVD_CDSC structure
> + * 1. first, the corresponding fields of the AVCodecContext structure are processed, (i.e -threads 4)
> + * 2. then xevd-specific options are added as AVOption to the xevd AVCodec implementation (i.e -threads 3)
> + * 3. finally, the options specified after the xevd-params option as the parameter list of type key value are processed (i.e -xevd-params "m=2")

I don't see a xevd-params option.

> + *
> + * Some options can be set in different ways. In this case, please follow the above-mentioned order of processing.
> + * The most recent assignments overwrite the previous values.
> + *
> + * @param[in] avctx codec context
> + * @param[out] cdsc contains all encoder parameters that should be initialized before its use
> + *
> + * @return 0 on success, negative error code on failure

I don't see a failure path below, so might as well just make this a void 
function.

> + */
> +static int get_conf(AVCodecContext *avctx, XEVD_CDSC *cdsc)
> +{
> +    int cpu_count = av_cpu_count();
> +
> +    /* clear XEVS_CDSC structure */
> +    memset(cdsc, 0, sizeof(XEVD_CDSC));
> +
> +    /* init XEVD_CDSC */
> +    if (avctx->thread_count <= 0)
> +        cdsc->threads = (cpu_count < XEVD_MAX_TASK_CNT) ? cpu_count : XEVD_MAX_TASK_CNT;
> +    else if (avctx->thread_count > XEVD_MAX_TASK_CNT)
> +        cdsc->threads = XEVD_MAX_TASK_CNT;
> +    else
> +        cdsc->threads = avctx->thread_count;
> +
> +    return 0;
> +}
> +
> +/**
> + * Read NAL unit length
> + * @param bs input data (bitstream)
> + * @return the length of NAL unit on success, 0 value on failure
> + */
> +static uint32_t read_nal_unit_length(const uint8_t *bs, int bs_size, AVCodecContext *avctx)
> +{
> +    uint32_t len = 0;
> +    XEVD_INFO info;
> +    int ret;
> +
> +    if (bs_size == XEVD_NAL_UNIT_LENGTH_BYTE) {
> +        ret = xevd_info((void *)bs, XEVD_NAL_UNIT_LENGTH_BYTE, 1, &info);
> +        if (XEVD_FAILED(ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information\n");
> +            return 0;
> +        }
> +        len = info.nalu_len;
> +        if (len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size! [%d]\n", bs_size);
> +            return 0;
> +        }
> +    }
> +
> +    return len;
> +}
> +
> +/**
> + * @param[in] xectx the structure that stores all the state associated with the instance of Xeve MPEG-5 EVC decoder
> + * @param[out] avctx codec context
> + * @return 0 on success, negative value on failure
> + */
> +static int export_stream_params(const XevdContext *xectx, AVCodecContext *avctx)
> +{
> +    int ret;
> +    int size;
> +    int color_space;
> +
> +    avctx->pix_fmt = AV_PIX_FMT_YUV420P10;
> +
> +    size = 4;
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_WIDTH, &avctx->coded_width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_HEIGHT, &avctx->coded_height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_WIDTH, &avctx->width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_HEIGHT, &avctx->height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_COLOR_SPACE, &color_space, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get color_space\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +    switch(color_space) {
> +    case XEVD_CS_YCBCR400_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +        break;
> +    case XEVD_CS_YCBCR420_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +        break;
> +    case XEVD_CS_YCBCR422_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +        break;
> +    case XEVD_CS_YCBCR444_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +        break;
> +    default:
> +        av_log(avctx, AV_LOG_ERROR, "Unknown color space\n");
> +        avctx->pix_fmt = AV_PIX_FMT_NONE;
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    // the function returns sps->num_reorder_pics
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_MAX_CODING_DELAY, &avctx->max_b_frames, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get max_coding_delay\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    avctx->has_b_frames = (avctx->max_b_frames) ? 1 : 0;
> +
> +    avctx->color_primaries = AVCOL_PRI_UNSPECIFIED;
> +    avctx->color_trc       = AVCOL_TRC_UNSPECIFIED;
> +    avctx->colorspace      = AVCOL_SPC_UNSPECIFIED;
> +
> +    return 0;
> +}
> +
> +/**
> + * Initialize decoder
> + * Create a decoder instance and allocate all the needed resources
> + *
> + * @param avctx codec context
> + * @return 0 on success, negative error code on failure
> + */
> +static av_cold int libxevd_init(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    int ret = 0;
> +    XEVD_CDSC *cdsc = &(xectx->cdsc);
> +
> +    /* read configurations and set values for created descriptor (XEVD_CDSC) */
> +    ret = get_conf(avctx, cdsc);
> +    if (ret != 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot get configuration\n");
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    /* create decoder */
> +    xectx->id = xevd_create(&(xectx->cdsc), NULL);
> +    if (xectx->id == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot create XEVD encoder\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    xectx->packet_count = 0;
> +    xectx->decod_frames = 0;
> +
> +    return 0;
> +}
> +
> +/**
> +  * Decode picture
> +  *
> +  * @param avctx codec context
> +  * @param[out] frame decoded frame
> +  * @param[out] got_frame_ptr decoder sets to 0 or 1 to indicate that a
> +  *                       non-empty frame or subtitle was returned in
> +  *                       outdata.
> +  * @param[in] avpkt AVPacket containing encoded data to be decoded
> +  *
> +  * @return amount of bytes read from the packet on success, negative error
> +  *         code on failure
> +  */
> +static int libxevd_decode(struct AVCodecContext *avctx, struct AVFrame *frame, int *got_frame_ptr, AVPacket *avpkt)
> +{
> +    XevdContext *xectx = NULL;
> +    XEVD_IMGB *imgb = NULL;
> +    XEVD_STAT stat;
> +    XEVD_BITB bitb;
> +    int xevd_ret, nalu_size, bs_read_pos;
> +    int ret = 0;
> +
> +    if (avctx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid input parameter: AVCodecContext\n");
> +        return AVERROR(EINVAL);
> +    }
> +    xectx = avctx->priv_data;
> +    if (xectx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid XEVD context\n");
> +        return AVERROR(EINVAL);

This can't happen, just remove the check.

> +    }
> +
> +    if (avpkt->size > 0) {
> +        bs_read_pos = 0;
> +        imgb = NULL;
> +        while(avpkt->size > (bs_read_pos + XEVD_NAL_UNIT_LENGTH_BYTE)) {
> +
> +            memset(&stat, 0, sizeof(XEVD_STAT));
> +            memset(&bitb, 0, sizeof(XEVD_BITB));
> +
> +            nalu_size = read_nal_unit_length(avpkt->data + bs_read_pos, XEVD_NAL_UNIT_LENGTH_BYTE, avctx);
> +            if (nalu_size == 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Invalid bitstream\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +            bs_read_pos += XEVD_NAL_UNIT_LENGTH_BYTE;
> +
> +            bitb.addr = avpkt->data + bs_read_pos;
> +            bitb.ssize = nalu_size;
> +
> +            /* main decoding block */
> +            xevd_ret = xevd_decode(xectx->id, &bitb, &stat);
> +            if (XEVD_FAILED(xevd_ret)) {
> +                av_log(avctx, AV_LOG_ERROR, "Failed to decode bitstream\n");
> +                ret = AVERROR_EXTERNAL;
> +                goto ERR;
> +            }
> +
> +            bs_read_pos += nalu_size;
> +
> +            if (stat.nalu_type == XEVD_NUT_SPS) { // EVC stream parameters changed
> +                if ((ret = export_stream_params(xectx, avctx)) != 0)
> +                    goto ERR;
> +            }
> +
> +            if (stat.read != nalu_size)
> +                av_log(avctx, AV_LOG_INFO, "Different reading of bitstream (in:%d,read:%d)\n,", nalu_size, stat.read);
> +            if (stat.fnum >= 0) {
> +                // already has a decoded image
> +                if (imgb) {
> +                    // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                    // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                    imgb->release(imgb);
> +                    imgb = NULL;
> +                }
> +                xevd_ret = xevd_pull(xectx->id, &imgb);
> +                if (XEVD_FAILED(xevd_ret)) {
> +                    av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d, frame#=%d)\n", xevd_ret, stat.fnum);
> +                    ret = AVERROR_EXTERNAL;
> +                    goto ERR;
> +                } else if (xevd_ret == XEVD_OK_FRM_DELAYED) {
> +                    if (imgb) {
> +                        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                        imgb->release(imgb);
> +                        imgb = NULL;
> +                    }
> +                }

So if the packet has more than one frame, you'll drop the oldest?

Maybe you should write this decoder using the decouple Input/Output API, 
FF_CODEC_RECEIVE_FRAME_CB() callback instead of FF_CODEC_DECODE_CB().
With it, you can request a packet as needed with ff_decode_get_packet(), 
so for example only when libxevd has run out of frames to output you 
actually request another.

> +            }
> +        }
> +    } else { // bumping
> +        xevd_ret = xevd_pull(xectx->id, &(imgb));
> +        if (xevd_ret == XEVD_ERR_UNEXPECTED) { // bumping process completed

Shouldn't this be XEVD_OK_NO_MORE_FRM?

> +            *got_frame_ptr = 0;
> +            return 0;
> +        } else if (XEVD_FAILED(xevd_ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d)\n", xevd_ret);
> +            ret = AVERROR_EXTERNAL;
> +            goto ERR;
> +        }
> +    }
> +
> +    if (imgb) {
> +        // @todo supports other color space and bit depth
> +        if (imgb->cs != XEVD_CS_YCBCR420_10LE) {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported pixel format: %s\n", av_get_pix_fmt_name(avctx->pix_fmt));
> +            ret = AVERROR_INVALIDDATA;
> +            goto ERR;
> +        }
> +
> +        if (imgb->w[0] != avctx->width || imgb->h[0] != avctx->height) { // stream resolution changed
> +            if (ff_set_dimensions(avctx, imgb->w[0], imgb->h[0]) < 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Cannot set new dimension\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +        }
> +
> +        frame->coded_picture_number++;
> +        frame->display_picture_number++;

As is, these two will always be 1. If you want to set these fields, you 
need to keep track of total decoded frames elsewhere.
stat.fnum looks like what you need, or maybe xectx->decod_frames.

> +        frame->format = AV_PIX_FMT_YUV420P10LE;

No need to set this here. ff_get_buffer() will handle it for you.

> +
> +        if (ff_get_buffer(avctx, frame, 0) < 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get AV buffer\n");

ff_get_buffer() already prints an error, so remove this one.

> +            ret = AVERROR(ENOMEM);

It also returns an error code you should propagate.

> +            goto ERR;
> +        }
> +
> +        frame->pts = avpkt->pts;
> +
> +        av_image_copy(frame->data, frame->linesize, (const uint8_t **)imgb->a,
> +                      imgb->s, avctx->pix_fmt,
> +                      imgb->w[0], imgb->h[0]);
> +
> +        xectx->decod_frames++;

Write only variable.

> +        *got_frame_ptr = 1;
> +
> +        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    } else
> +        *got_frame_ptr = 0;
> +
> +    xectx->packet_count++;

Same.

> +
> +    return avpkt->size;
> +
> +ERR:
> +    if (imgb) {
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    }
> +    *got_frame_ptr = 0;
> +
> +    return ret;
> +}
> +
> +/**
> + * Destroy decoder
> + *
> + * @param avctx codec context
> + * @return 0 on success
> + */
> +static av_cold int libxevd_close(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    if (xectx->id) {
> +        xevd_delete(xectx->id);
> +        xectx->id = NULL;
> +    }
> +
> +    return 0;
> +}
> +
> +#define OFFSET(x) offsetof(XevdContext, x)
> +#define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
> +
> +static const AVClass libxevd_class = {
> +    .class_name = "libxevd",
> +    .item_name  = av_default_item_name,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> +const FFCodec ff_libxevd_decoder = {
> +    .p.name             = "evc",
> +    .p.long_name        = NULL_IF_CONFIG_SMALL("EVC / MPEG-5 Essential Video Coding (EVC)"),
> +    .p.type             = AVMEDIA_TYPE_VIDEO,
> +    .p.id               = AV_CODEC_ID_EVC,
> +    .init               = libxevd_init,
> +    FF_CODEC_DECODE_CB(libxevd_decode),
> +    .close              = libxevd_close,
> +    .priv_data_size     = sizeof(XevdContext),
> +    .p.priv_class       = &libxevd_class,
> +    .p.capabilities     = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AUTO_THREADS | AV_CODEC_CAP_AVOID_PROBING | AV_CODEC_CAP_DR1,

Use AV_CODEC_CAP_OTHER_THREADS, not AV_CODEC_CAP_AUTO_THREADS.
And set caps_internal to FF_CODEC_CAP_AUTO_THREADS.

> +    .p.wrapper_name     = "libxevd",
> +};

I've  just submitted new patches that were made based on your requests and suggestions.
Please find below my comments.

-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James Almer
Sent: Monday, August 1, 2022 2:29 PM
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/2] Provided support for MPEG-5 EVC (Essential Video Coding) codec

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/evc_parser.c b/libavcodec/evc_parser.c
> new file mode 100644
> index 0000000000..b2136a6b45
> --- /dev/null
> +++ b/libavcodec/evc_parser.c
> @@ -0,0 +1,526 @@
> +/*
> + * EVC format parser
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <stdint.h>
> +
> +#include "libavutil/common.h"
> +
> +#include "parser.h"
> +#include "golomb.h"
> +
> +// The length field that indicates the length in bytes of the following NAL unit is configured to be of 4 bytes
> +#define EVC_NAL_UNIT_LENGTH_BYTE        (4)  /* byte */
> +
> +#define EVC_NAL_HEADER_SIZE             (2)  /* byte */
> +#define MAX_SPS_CNT                     (16) /* defined value in EVC standard */
> +
> +// NALU types
> +// @see ISO_IEC_23094-1_2020 7.4.2.2 NAL unit header semantics
> +//
> +#define EVC_NUT_NONIDR                  (0)  /* Coded slice of a non-IDR picture */
> +#define EVC_NUT_IDR                     (1)  /* Coded slice of an IDR picture */
> +#define EVC_NUT_SPS                     (24) /* Sequence parameter set */
> +#define EVC_NUT_PPS                     (25) /* Picture paremeter set */
> +#define EVC_NUT_APS                     (26) /* Adaptation parameter set */
> +#define EVC_NUT_FD                      (27) /* Filler data */
> +#define EVC_NUT_SEI                     (28) /* Supplemental enhancement information */
> +
> +// The sturcture reflects SPS RBSP(raw byte sequence payload) layout
> +// @see ISO_IEC_23094-1 section 7.3.2.1
> +//
> +// The following descriptors specify the parsing process of each element
> +// u(n) - unsigned integer using n bits
> +// ue(v) - unsigned integer 0-th order Exp_Golomb-coded syntax element with the left bit first
> +typedef struct EVCParserSPS {
> +    int sps_seq_parameter_set_id;   // ue(v)
> +    int profile_idc;                // u(8)
> +    int level_idc;                  // u(8)
> +    int toolset_idc_h;              // u(32)
> +    int toolset_idc_l;              // u(32)
> +    int chroma_format_idc;          // ue(v)
> +    int pic_width_in_luma_samples;  // ue(v)
> +    int pic_height_in_luma_samples; // ue(v)
> +    int bit_depth_luma_minus8;      // ue(v)
> +    int bit_depth_chroma_minus8;    // ue(v)
> +
> +    int sps_btt_flag;                           // u(1)
> +    int log2_ctu_size_minus5;                   // ue(v)
> +    int log2_min_cb_size_minus2;                // ue(v)
> +    int log2_diff_ctu_max_14_cb_size;           // ue(v)
> +    int log2_diff_ctu_max_tt_cb_size;           // ue(v)
> +    int log2_diff_min_cb_min_tt_cb_size_minus2; // ue(v)
> +
> +    int sps_suco_flag;                       // u(1)
> +    int log2_diff_ctu_size_max_suco_cb_size; // ue(v)
> +    int log2_diff_max_suco_min_suco_cb_size; // ue(v)
> +
> +    int sps_admvp_flag;     // u(1)
> +    int sps_affine_flag;    // u(1)
> +    int sps_amvr_flag;      // u(1)
> +    int sps_dmvr_flag;      // u(1)
> +    int sps_mmvd_flag;      // u(1)
> +    int sps_hmvp_flag;      // u(1)
> +
> +    int sps_eipd_flag;                 // u(1)
> +    int sps_ibc_flag;                  // u(1)
> +    int log2_max_ibc_cand_size_minus2; // ue(v)
> +
> +    int sps_cm_init_flag; // u(1)
> +    int sps_adcc_flag;    // u(1)
> +
> +    int sps_iqt_flag; // u(1)
> +    int sps_ats_flag; // u(1)
> +
> +    int sps_addb_flag;   // u(1)
> +    int sps_alf_flag;    // u(1)
> +    int sps_htdf_flag;   // u(1)
> +    int sps_rpl_flag;    // u(1)
> +    int sps_pocs_flag;   // u(1)
> +    int sps_dquant_flag; // u(1)
> +    int sps_dra_flag;    // u(1)
> +
> +    int log2_max_pic_order_cnt_lsb_minus4; // ue(v)
> +    int log2_sub_gop_length;               // ue(v)
> +    int log2_ref_pic_gap_length;           // ue(v)
> +
> +    int max_num_tid0_ref_pics; // ue(v)
> +
> +    int sps_max_dec_pic_buffering_minus1; // ue(v)
> +    int long_term_ref_pic_flag;           // u(1)
> +    int rpl1_same_as_rpl0_flag;           // u(1)
> +    int num_ref_pic_list_in_sps[2];       // ue(v)
> +
> +    int picture_cropping_flag;      // u(1)
> +    int picture_crop_left_offset;   // ue(v)
> +    int picture_crop_right_offset;  // ue(v)
> +    int picture_crop_top_offset;    // ue(v)
> +    int picture_crop_bottom_offset; // ue(v)
> +
> +} EVCParserSPS;
> +
> +typedef struct EVCParserContext {
> +    ParseContext pc;
> +    EVCParserSPS sps[MAX_SPS_CNT];
> +    int is_avc;
> +    int nal_length_size;
> +    int to_read;
> +    int incomplete_nalu_prefix_read; // The flag is set to 1 when an incomplete NAL unit prefix has been read
> +
> +    int got_sps;
> +    int got_pps;
> +    int got_sei;
> +    int got_slice;
> +} EVCParserContext;
> +
> +static int get_nalu_type(const uint8_t *bits, int bits_size, AVCodecContext *avctx)
> +{
> +    int unit_type_plus1 = 0;
> +
> +    if(bits_size >= EVC_NAL_HEADER_SIZE) {
> +        unsigned char *p = (unsigned char *)bits;
> +        // forbidden_zero_bit
> +        if ((p[0] & 0x80) != 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information. Malformed bitstream.\n");
> +            return -1;
> +        }
> +
> +        // nal_unit_type
> +        unit_type_plus1 = (p[0] >> 1) & 0x3F;
> +    }
> +
> +    return unit_type_plus1 - 1;
> +}
> +
> +static uint32_t read_nal_unit_length(const uint8_t *bits, int bits_size, AVCodecContext *avctx)
> +{
> +    uint32_t nalu_len = 0;
> +
> +    if(bits_size >= EVC_NAL_UNIT_LENGTH_BYTE) {
> +
> +        int t = 0;
> +        unsigned char *p = (unsigned char *)bits;
> +
> +        for(int i = 0; i < EVC_NAL_UNIT_LENGTH_BYTE; i++)
> +            t = (t << 8) | p[i];
> +
> +        nalu_len = t;
> +        if(nalu_len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size!\n");
> +            return 0;
> +        }
> +    }
> +
> +    return nalu_len;
> +}
> +
> +// @see ISO_IEC_23094-1 (7.3.2.1 SPS RBSP syntax)
> +static EVCParserSPS *parse_sps(const uint8_t *bs, int bs_size, EVCParserContext *ev)
> +{
> +    GetBitContext gb;
> +    EVCParserSPS *sps;
> +    int sps_seq_parameter_set_id;
> +
> +    if(init_get_bits8(&gb, bs, bs_size) < 0)
> +        return NULL;
> +
> +    sps_seq_parameter_set_id = get_ue_golomb(&gb);
> +
> +    if(sps_seq_parameter_set_id >= MAX_SPS_CNT)
> +        return NULL;
> +
> +    sps = &ev->sps[sps_seq_parameter_set_id];
> +    sps->sps_seq_parameter_set_id = sps_seq_parameter_set_id;
> +
> +    // the Baseline profile is indicated by profile_idc eqal to 0
> +    // the Main profile is indicated by profile_idc eqal to 1
> +    sps->profile_idc = get_bits(&gb, 8);
> +
> +    sps->level_idc = get_bits(&gb, 8);
> +
> +    skip_bits_long(&gb, 32); /* skip toolset_idc_h */
> +    skip_bits_long(&gb, 32); /* skip toolset_idc_l */
> +
> +    // 0 - monochrome
> +    // 1 - 4:2:0
> +    // 2 - 4:2:2
> +    // 3 - 4:4:4
> +    sps->chroma_format_idc = get_ue_golomb(&gb);
> +
> +    sps->pic_width_in_luma_samples = get_ue_golomb(&gb);
> +    sps->pic_height_in_luma_samples = get_ue_golomb(&gb);
> +
> +    sps->bit_depth_luma_minus8 = get_ue_golomb(&gb);
> +    sps->bit_depth_chroma_minus8 = get_ue_golomb(&gb);
> +
> +    sps->sps_btt_flag = get_bits(&gb, 1);
> +    if(sps->sps_btt_flag) {
> +        sps->log2_ctu_size_minus5 = get_ue_golomb(&gb);
> +        sps->log2_min_cb_size_minus2 = get_ue_golomb(&gb);
> +        sps->log2_diff_ctu_max_14_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_ctu_max_tt_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_min_cb_min_tt_cb_size_minus2 = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_suco_flag = get_bits(&gb, 1);
> +    if(sps->sps_suco_flag) {
> +        sps->log2_diff_ctu_size_max_suco_cb_size = get_ue_golomb(&gb);
> +        sps->log2_diff_max_suco_min_suco_cb_size = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_admvp_flag = get_bits(&gb, 1);
> +    if(sps->sps_admvp_flag) {
> +        sps->sps_affine_flag = get_bits(&gb, 1);
> +        sps->sps_amvr_flag = get_bits(&gb, 1);
> +        sps->sps_dmvr_flag = get_bits(&gb, 1);
> +        sps->sps_mmvd_flag = get_bits(&gb, 1);
> +        sps->sps_hmvp_flag = get_bits(&gb, 1);
> +    }
> +
> +    sps->sps_eipd_flag =  get_bits(&gb, 1);
> +    if(sps->sps_eipd_flag) {
> +        sps->sps_ibc_flag = get_bits(&gb, 1);
> +        if(sps->sps_ibc_flag)
> +            sps->log2_max_ibc_cand_size_minus2 = get_ue_golomb(&gb);
> +    }
> +
> +    sps->sps_cm_init_flag = get_bits(&gb, 1);
> +    if(sps->sps_cm_init_flag)
> +        sps->sps_adcc_flag = get_bits(&gb, 1);
> +
> +    sps->sps_iqt_flag = get_bits(&gb, 1);
> +    if(sps->sps_iqt_flag)
> +        sps->sps_ats_flag = get_bits(&gb, 1);
> +
> +    sps->sps_addb_flag = get_bits(&gb, 1);
> +    sps->sps_alf_flag = get_bits(&gb, 1);
> +    sps->sps_htdf_flag = get_bits(&gb, 1);
> +    sps->sps_rpl_flag = get_bits(&gb, 1);
> +    sps->sps_pocs_flag = get_bits(&gb, 1);
> +    sps->sps_dquant_flag = get_bits(&gb, 1);
> +    sps->sps_dra_flag = get_bits(&gb, 1);
> +
> +    if(sps->sps_pocs_flag)
> +        sps->log2_max_pic_order_cnt_lsb_minus4 = get_ue_golomb(&gb);
> +
> +    if(!sps->sps_pocs_flag || !sps->sps_rpl_flag) {
> +        sps->log2_sub_gop_length = get_ue_golomb(&gb);
> +        if(sps->log2_sub_gop_length == 0)
> +            sps->log2_ref_pic_gap_length = get_ue_golomb(&gb);
> +    }
> +
> +    return sps;
> +}
> +
> +static int parse_nal_units(AVCodecParserContext *s, const uint8_t *bs,
> +                           int bs_size, AVCodecContext *avctx)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +    int nalu_type, nalu_size;
> +    unsigned char *bits = (unsigned char *)bs;
> +    int bits_size = bs_size;
> +
> +    avctx->codec_id = AV_CODEC_ID_EVC;
> +
> +    nalu_size = read_nal_unit_length(bits, bits_size, avctx);
> +    if(nalu_size == 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit size: (%d)\n", nalu_size);
> +        return -1;
> +    }
> +
> +    bits += EVC_NAL_UNIT_LENGTH_BYTE;
> +    bits_size -= EVC_NAL_UNIT_LENGTH_BYTE;
> +
> +    nalu_type = get_nalu_type(bits, bits_size, avctx);
> +
> +    bits += EVC_NAL_HEADER_SIZE;
> +    bits_size -= EVC_NAL_HEADER_SIZE;
> +
> +    if (nalu_type == EVC_NUT_SPS) { // NAL Unit type: SPS (Sequence Parameter Set)
> +        EVCParserSPS *sps;
> +
> +        sps = parse_sps(bits, bits_size, ev);
> +
> +        avctx->coded_width         = sps->pic_width_in_luma_samples;
> +        avctx->coded_height        = sps->pic_height_in_luma_samples;
> +        avctx->width               = sps->pic_width_in_luma_samples;
> +        avctx->height              = sps->pic_height_in_luma_samples;

These should be set in the AVCodecParserContext, not the AVCodecContext.
####################
DONE
####################
> +
> +        if(sps->profile_idc == 0) avctx->profile = FF_PROFILE_EVC_BASELINE;
> +        else if (sps->profile_idc == 1) avctx->profile = FF_PROFILE_EVC_MAIN;

Setting these two is ok.

> +        else {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported profile (%d)\n", sps->profile_idc);
> +            return -1;

Do you really need to abort here? Not recognizing the profile can't 
possibly mean the bitstream can't be parsed further to fetch other 
information.
####################
DONE
####################
> +        }
> +
> +        // Currently XEVD decoder supports ony YCBCR420_10LE chroma format for EVC stream
> +        switch(sps->chroma_format_idc) {
> +        case 0: /* YCBCR400_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR400_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +            return -1;
> +        case 1: /* YCBCR420_10LE */
> +            avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +            break;
> +        case 2: /* YCBCR422_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR422_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +            return -1;
> +        case 3: /* YCBCR444_10LE */
> +            av_log(avctx, AV_LOG_ERROR, "YCBCR444_10LE: Not supported chroma format\n");
> +            avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +            return -1;
> +        default:
> +            avctx->pix_fmt = AV_PIX_FMT_NONE;

Fill s->format instead of avctx->pix_fmt.
####################
DONE
####################
> +            av_log(avctx, AV_LOG_ERROR, "Unknown supported chroma format\n");
> +            return -1;
> +        }
> +
> +        // The current implementation of parse_sps function doesn't handle VUI parameters parsing,
> +        // so at the moment it's impossible to initialize has_b_frames and max_b_frames AVCodecContex fields here.
> +        // Currently, initialization of has_b_frames and max_b_frames AVCodecContex fields have been moved to
> +        // libxevd_decode function where we can use xevd_config function being a part of xevd library API
> +        // to get the needed information.
> +        // However, if it will be needed, parse_sps function should be extended to handle VUI parameters parsing
> +        // and the following lines should be used to initialize has_b_frames and max_b_frames fields of the AVCodecContex.

There's no need no fill any of those field in this parser. What you can 
fill is avctx->color{space,_primaries,_trc,_range}, so mention that to 
add VUI parsing at some point.

> +        //
> +        // sps->vui_parameters.num_reorder_pics
> +        // if (sps->bitstream_restriction_flag && sps->vui_parameters.num_reorder_pics) {
> +        //     avctx->has_b_frames = sps->vui_parameters.num_reorder_pics;
> +        // }
> +
> +        ev->got_sps = 1;
> +
> +    } else if (nalu_type == EVC_NUT_PPS) // NAL Unit type: PPS (Video Parameter Set)
> +        ev->got_pps = 1;
> +    else if(nalu_type == EVC_NUT_SEI) // NAL unit type: SEI (Supplemental Enhancement Information)
> +        ev->got_sei = 1;

These got_* variables seem to be write only.
####################
DONE
####################
> +    else if (nalu_type == EVC_NUT_IDR || nalu_type == EVC_NUT_NONIDR) // NAL Unit type: Coded slice of a IDR or non-IDR picture

In here you should parse enough data to get the picture type (I, P, B) 
and set s->pict_type, and based on (i suppose) nalu_type, also set 
s->key_frame to 1 or 0.
####################
DONE
####################

At the start of this function, you'd ideally set them to 
AV_PICTURE_TYPE_NONE and -1 respectively, as "safe" defaults.
####################
DONE
####################

s->picture_structure should also be always set to 
AV_PICTURE_STRUCTURE_FRAME, as i assume this codec does not support 
interlacing.
####################
DONE
####################

> +        ev->got_slice++;
> +    else {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit type: %d\n", nalu_type);
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +/**
> + * Find the end of the current frame in the bitstream.
> + * @return the position of the first byte of the next frame, or END_NOT_FOUND
> + */
> +static int evc_find_frame_end(AVCodecParserContext *s, const uint8_t *buf,
> +                              int buf_size, AVCodecContext *avctx)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +
> +    if(!ev->to_read) {
> +        int nal_unit_size = 0;
> +        int next = END_NOT_FOUND;
> +
> +        // This is the case when buffer size is not enough for buffer to store NAL unit length
> +        if(buf_size < EVC_NAL_UNIT_LENGTH_BYTE) {
> +            ev->to_read = EVC_NAL_UNIT_LENGTH_BYTE;
> +            ev->nal_length_size = buf_size;
> +            ev->incomplete_nalu_prefix_read  = 1;
> +
> +            return END_NOT_FOUND;
> +        }
> +
> +        nal_unit_size = read_nal_unit_length(buf, buf_size, avctx);
> +        ev->nal_length_size = EVC_NAL_UNIT_LENGTH_BYTE;
> +
> +        next = nal_unit_size + EVC_NAL_UNIT_LENGTH_BYTE;
> +        ev->to_read = next;
> +        if(next < buf_size)
> +            return next;
> +        else
> +            return END_NOT_FOUND;
> +    } else if(ev->to_read > buf_size)
> +        return END_NOT_FOUND;
> +    else {
> +        if(ev->incomplete_nalu_prefix_read  == 1) {
> +            EVCParserContext *ev = s->priv_data;
> +            ParseContext *pc = &ev->pc;
> +            uint8_t nalu_len[EVC_NAL_UNIT_LENGTH_BYTE] = {0};
> +            int nal_unit_size = 0;
> +
> +            // 1. pc->buffer contains previously read bytes of NALU prefix
> +            // 2. buf contains the rest of NAL unit prefix bytes
> +            //
> +            // ~~~~~~~
> +            // EXAMPLE
> +            // ~~~~~~~
> +            //
> +            // In the following example we assumed that the number of already read NAL Unit prefix bytes is equal 1
> +            //
> +            // ----------
> +            // pc->buffer -> conatins already read bytes
> +            // ----------
> +            //              __ pc->index == 1
> +            //             |
> +            //             V
> +            // -------------------------------------------------------
> +            // |   0   |   1   |   2   |   3   |   4   | ... |   N   |
> +            // -------------------------------------------------------
> +            // |  0x00 |  0xXX |  0xXX |  0xXX |  0xXX | ... |  0xXX |
> +            // -------------------------------------------------------
> +            //
> +            // ----------
> +            // buf -> contains newly read bytes
> +            // ----------
> +            // -------------------------------------------------------
> +            // |   0   |   1   |   2   |   3   |   4   | ... |   N   |
> +            // -------------------------------------------------------
> +            // |  0x00 |  0x00 |  0x3C |  0xXX |  0xXX | ... |  0xXX |
> +            // -------------------------------------------------------
> +            //
> +            for(int i = 0; i < EVC_NAL_UNIT_LENGTH_BYTE; i++) {
> +                if(i < pc->index)
> +                    nalu_len[i] = pc->buffer[i];
> +                else
> +                    nalu_len[i] = buf[i - pc->index];
> +            }
> +
> +            // ----------
> +            // nalu_len
> +            // ----------
> +            // ---------------------------------
> +            // |   0   |   1   |   2   |   3   |
> +            // ---------------------------------
> +            // |  0x00 |  0x00 |  0x00 |  0x3C |
> +            // ---------------------------------
> +            // | NALU LENGTH                   |
> +            // ---------------------------------
> +            // NAL Unit lenght =  60 (0x0000003C)
> +
> +            nal_unit_size = read_nal_unit_length(nalu_len, EVC_NAL_UNIT_LENGTH_BYTE, avctx);
> +
> +            ev->to_read = nal_unit_size + EVC_NAL_UNIT_LENGTH_BYTE - pc->index;
> +
> +            ev->incomplete_nalu_prefix_read = 0;
> +
> +            if(ev->to_read > buf_size)
> +                return END_NOT_FOUND;
> +            else
> +                return ev->to_read;
> +        }
> +        return ev->to_read;
> +    }
> +
> +    return END_NOT_FOUND;
> +}
> +
> +static int evc_parser_init(AVCodecParserContext *s)
> +{
> +    EVCParserContext *ev = s->priv_data;
> +
> +    ev->got_sps = 0;
> +    ev->got_pps = 0;
> +    ev->got_sei = 0;
> +    ev->got_slice = 0;
> +    ev->nal_length_size = EVC_NAL_UNIT_LENGTH_BYTE;
> +    ev->incomplete_nalu_prefix_read = 0;
> +
> +    return 0;
> +}
> +
> +static int evc_parse(AVCodecParserContext *s, AVCodecContext *avctx,
> +                     const uint8_t **poutbuf, int *poutbuf_size,
> +                     const uint8_t *buf, int buf_size)
> +{
> +    int next;
> +    EVCParserContext *ev = s->priv_data;
> +    ParseContext *pc = &ev->pc;
> +    int is_dummy_buf = !buf_size;
> +    const uint8_t *dummy_buf = buf;
> +
> +    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES)
> +        next = buf_size;
> +    else {
> +        next = evc_find_frame_end(s, buf, buf_size, avctx);
> +        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
> +            *poutbuf      = NULL;
> +            *poutbuf_size = 0;
> +            ev->to_read -= buf_size;
> +            return buf_size;
> +        }
> +    }
> +
> +    is_dummy_buf &= (dummy_buf == buf);
> +
> +    if (!is_dummy_buf)
> +        parse_nal_units(s, buf, buf_size, avctx);
> +
> +    *poutbuf      = buf;
> +    *poutbuf_size = buf_size;
> +    ev->to_read -= next;
> +
> +    return next;
> +}
> +
> +const AVCodecParser ff_evc_parser = {
> +    .codec_ids      = { AV_CODEC_ID_EVC },
> +    .priv_data_size = sizeof(EVCParserContext),
> +    .parser_init    = evc_parser_init,
> +    .parser_parse   = evc_parse,
> +    .parser_close   = ff_parse_close,
> +};

I just uploaded new patches that were made based on your requests and suggestions.
Please find below my comments.

-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James Almer
Sent: Monday, August 1, 2022 5:09 PM
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/2] Provided support for MPEG-5 EVC (Essential Video Coding) codec

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/libxevd.c b/libavcodec/libxevd.c
> new file mode 100644
> index 0000000000..8ba2d89cbd
> --- /dev/null
> +++ b/libavcodec/libxevd.c
> @@ -0,0 +1,436 @@
> +/*
> + * libxevd decoder
> + * EVC (MPEG-5 Essential Video Coding) decoding using XEVD MPEG-5 EVC decoder library
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <float.h>
> +#include <stdlib.h>
> +
> +#include <xevd.h>
> +
> +#include "libavutil/internal.h"
> +#include "libavutil/common.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/pixdesc.h"
> +#include "libavutil/pixfmt.h"
> +#include "libavutil/imgutils.h"
> +#include "libavutil/cpu.h"
> +
> +#include "avcodec.h"
> +#include "internal.h"
> +#include "packet_internal.h"
> +#include "codec_internal.h"
> +
> +#define XEVD_PARAM_BAD_NAME -1
> +#define XEVD_PARAM_BAD_VALUE -2
> +
> +#define EVC_NAL_HEADER_SIZE 2 /* byte */
> +
> +/**
> + * The structure stores all the states associated with the instance of Xeve MPEG-5 EVC decoder
> + */
> +typedef struct XevdContext {
> +    const AVClass *class;
> +
> +    XEVD id;            // XEVD instance identifier @see xevd.h
> +    XEVD_CDSC cdsc;     // decoding parameters @see xevd.h
> +
> +    int decod_frames;   // number of decoded frames
> +    int packet_count;   // number of packets created by decoder
> +} XevdContext;
> +
> +/**
> + * The function returns a pointer to a variable of type XEVD_CDSC.

This doesn't seem to be the case.
####################
DONE
####################

> + * XEVD_CDSC contains all decoder parameters that should be initialized before its use.
> + *
> + * The field values of the XEVD_CDSC structure are populated based on:
> + * - the corresponding field values of the AvCodecConetxt structure,
> + * - the xevd decoder specific option values,
> + *   (the full list of options available for the xevd encoder is displayed after executing the command ./ffmpeg --help decoder = libxevd)
> + * - and the xevd encoder options specified as a list of key-value pairs following the xevd-params option
> + *
> + * Order of input processing and populating the XEVD_CDSC structure
> + * 1. first, the corresponding fields of the AVCodecContext structure are processed, (i.e -threads 4)
> + * 2. then xevd-specific options are added as AVOption to the xevd AVCodec implementation (i.e -threads 3)
> + * 3. finally, the options specified after the xevd-params option as the parameter list of type key value are processed (i.e -xevd-params "m=2")

I don't see a xevd-params option.
####################
DONE
####################
> + *
> + * Some options can be set in different ways. In this case, please follow the above-mentioned order of processing.
> + * The most recent assignments overwrite the previous values.
> + *
> + * @param[in] avctx codec context
> + * @param[out] cdsc contains all encoder parameters that should be initialized before its use
> + *
> + * @return 0 on success, negative error code on failure

I don't see a failure path below, so might as well just make this a void 
function.
####################
DONE
####################

> + */
> +static int get_conf(AVCodecContext *avctx, XEVD_CDSC *cdsc)
> +{
> +    int cpu_count = av_cpu_count();
> +
> +    /* clear XEVS_CDSC structure */
> +    memset(cdsc, 0, sizeof(XEVD_CDSC));
> +
> +    /* init XEVD_CDSC */
> +    if (avctx->thread_count <= 0)
> +        cdsc->threads = (cpu_count < XEVD_MAX_TASK_CNT) ? cpu_count : XEVD_MAX_TASK_CNT;
> +    else if (avctx->thread_count > XEVD_MAX_TASK_CNT)
> +        cdsc->threads = XEVD_MAX_TASK_CNT;
> +    else
> +        cdsc->threads = avctx->thread_count;
> +
> +    return 0;
> +}
> +
> +/**
> + * Read NAL unit length
> + * @param bs input data (bitstream)
> + * @return the length of NAL unit on success, 0 value on failure
> + */
> +static uint32_t read_nal_unit_length(const uint8_t *bs, int bs_size, AVCodecContext *avctx)
> +{
> +    uint32_t len = 0;
> +    XEVD_INFO info;
> +    int ret;
> +
> +    if (bs_size == XEVD_NAL_UNIT_LENGTH_BYTE) {
> +        ret = xevd_info((void *)bs, XEVD_NAL_UNIT_LENGTH_BYTE, 1, &info);
> +        if (XEVD_FAILED(ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information\n");
> +            return 0;
> +        }
> +        len = info.nalu_len;
> +        if (len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size! [%d]\n", bs_size);
> +            return 0;
> +        }
> +    }
> +
> +    return len;
> +}
> +
> +/**
> + * @param[in] xectx the structure that stores all the state associated with the instance of Xeve MPEG-5 EVC decoder
> + * @param[out] avctx codec context
> + * @return 0 on success, negative value on failure
> + */
> +static int export_stream_params(const XevdContext *xectx, AVCodecContext *avctx)
> +{
> +    int ret;
> +    int size;
> +    int color_space;
> +
> +    avctx->pix_fmt = AV_PIX_FMT_YUV420P10;
> +
> +    size = 4;
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_WIDTH, &avctx->coded_width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_HEIGHT, &avctx->coded_height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_WIDTH, &avctx->width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_HEIGHT, &avctx->height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_COLOR_SPACE, &color_space, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get color_space\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +    switch(color_space) {
> +    case XEVD_CS_YCBCR400_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +        break;
> +    case XEVD_CS_YCBCR420_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +        break;
> +    case XEVD_CS_YCBCR422_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +        break;
> +    case XEVD_CS_YCBCR444_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +        break;
> +    default:
> +        av_log(avctx, AV_LOG_ERROR, "Unknown color space\n");
> +        avctx->pix_fmt = AV_PIX_FMT_NONE;
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    // the function returns sps->num_reorder_pics
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_MAX_CODING_DELAY, &avctx->max_b_frames, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get max_coding_delay\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    avctx->has_b_frames = (avctx->max_b_frames) ? 1 : 0;
> +
> +    avctx->color_primaries = AVCOL_PRI_UNSPECIFIED;
> +    avctx->color_trc       = AVCOL_TRC_UNSPECIFIED;
> +    avctx->colorspace      = AVCOL_SPC_UNSPECIFIED;
> +
> +    return 0;
> +}
> +
> +/**
> + * Initialize decoder
> + * Create a decoder instance and allocate all the needed resources
> + *
> + * @param avctx codec context
> + * @return 0 on success, negative error code on failure
> + */
> +static av_cold int libxevd_init(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    int ret = 0;
> +    XEVD_CDSC *cdsc = &(xectx->cdsc);
> +
> +    /* read configurations and set values for created descriptor (XEVD_CDSC) */
> +    ret = get_conf(avctx, cdsc);
> +    if (ret != 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot get configuration\n");
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    /* create decoder */
> +    xectx->id = xevd_create(&(xectx->cdsc), NULL);
> +    if (xectx->id == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot create XEVD encoder\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    xectx->packet_count = 0;
> +    xectx->decod_frames = 0;
> +
> +    return 0;
> +}
> +
> +/**
> +  * Decode picture
> +  *
> +  * @param avctx codec context
> +  * @param[out] frame decoded frame
> +  * @param[out] got_frame_ptr decoder sets to 0 or 1 to indicate that a
> +  *                       non-empty frame or subtitle was returned in
> +  *                       outdata.
> +  * @param[in] avpkt AVPacket containing encoded data to be decoded
> +  *
> +  * @return amount of bytes read from the packet on success, negative error
> +  *         code on failure
> +  */
> +static int libxevd_decode(struct AVCodecContext *avctx, struct AVFrame *frame, int *got_frame_ptr, AVPacket *avpkt)
> +{
> +    XevdContext *xectx = NULL;
> +    XEVD_IMGB *imgb = NULL;
> +    XEVD_STAT stat;
> +    XEVD_BITB bitb;
> +    int xevd_ret, nalu_size, bs_read_pos;
> +    int ret = 0;
> +
> +    if (avctx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid input parameter: AVCodecContext\n");
> +        return AVERROR(EINVAL);
> +    }
> +    xectx = avctx->priv_data;
> +    if (xectx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid XEVD context\n");
> +        return AVERROR(EINVAL);

This can't happen, just remove the check.
####################
DONE
####################

> +    }
> +
> +    if (avpkt->size > 0) {
> +        bs_read_pos = 0;
> +        imgb = NULL;
> +        while(avpkt->size > (bs_read_pos + XEVD_NAL_UNIT_LENGTH_BYTE)) {
> +
> +            memset(&stat, 0, sizeof(XEVD_STAT));
> +            memset(&bitb, 0, sizeof(XEVD_BITB));
> +
> +            nalu_size = read_nal_unit_length(avpkt->data + bs_read_pos, XEVD_NAL_UNIT_LENGTH_BYTE, avctx);
> +            if (nalu_size == 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Invalid bitstream\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +            bs_read_pos += XEVD_NAL_UNIT_LENGTH_BYTE;
> +
> +            bitb.addr = avpkt->data + bs_read_pos;
> +            bitb.ssize = nalu_size;
> +
> +            /* main decoding block */
> +            xevd_ret = xevd_decode(xectx->id, &bitb, &stat);
> +            if (XEVD_FAILED(xevd_ret)) {
> +                av_log(avctx, AV_LOG_ERROR, "Failed to decode bitstream\n");
> +                ret = AVERROR_EXTERNAL;
> +                goto ERR;
> +            }
> +
> +            bs_read_pos += nalu_size;
> +
> +            if (stat.nalu_type == XEVD_NUT_SPS) { // EVC stream parameters changed
> +                if ((ret = export_stream_params(xectx, avctx)) != 0)
> +                    goto ERR;
> +            }
> +
> +            if (stat.read != nalu_size)
> +                av_log(avctx, AV_LOG_INFO, "Different reading of bitstream (in:%d,read:%d)\n,", nalu_size, stat.read);
> +            if (stat.fnum >= 0) {
> +                // already has a decoded image
> +                if (imgb) {
> +                    // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                    // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                    imgb->release(imgb);
> +                    imgb = NULL;
> +                }
> +                xevd_ret = xevd_pull(xectx->id, &imgb);
> +                if (XEVD_FAILED(xevd_ret)) {
> +                    av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d, frame#=%d)\n", xevd_ret, stat.fnum);
> +                    ret = AVERROR_EXTERNAL;
> +                    goto ERR;
> +                } else if (xevd_ret == XEVD_OK_FRM_DELAYED) {
> +                    if (imgb) {
> +                        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                        imgb->release(imgb);
> +                        imgb = NULL;
> +                    }
> +                }

So if the packet has more than one frame, you'll drop the oldest?
####################
DONE
####################

Maybe you should write this decoder using the decouple Input/Output API, 
FF_CODEC_RECEIVE_FRAME_CB() callback instead of FF_CODEC_DECODE_CB().
With it, you can request a packet as needed with ff_decode_get_packet(), 
so for example only when libxevd has run out of frames to output you 
actually request another.

> +            }
> +        }
> +    } else { // bumping
> +        xevd_ret = xevd_pull(xectx->id, &(imgb));
> +        if (xevd_ret == XEVD_ERR_UNEXPECTED) { // bumping process completed

Shouldn't this be XEVD_OK_NO_MORE_FRM?
--------------------
No. It should't be XEVD_OK_NO_MORE_FRM. It means that bumping process has completed
--------------------

> +            *got_frame_ptr = 0;
> +            return 0;
> +        } else if (XEVD_FAILED(xevd_ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d)\n", xevd_ret);
> +            ret = AVERROR_EXTERNAL;
> +            goto ERR;
> +        }
> +    }
> +
> +    if (imgb) {
> +        // @todo supports other color space and bit depth
> +        if (imgb->cs != XEVD_CS_YCBCR420_10LE) {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported pixel format: %s\n", av_get_pix_fmt_name(avctx->pix_fmt));
> +            ret = AVERROR_INVALIDDATA;
> +            goto ERR;
> +        }
> +
> +        if (imgb->w[0] != avctx->width || imgb->h[0] != avctx->height) { // stream resolution changed
> +            if (ff_set_dimensions(avctx, imgb->w[0], imgb->h[0]) < 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Cannot set new dimension\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +        }
> +
> +        frame->coded_picture_number++;
> +        frame->display_picture_number++;

As is, these two will always be 1. If you want to set these fields, you 
need to keep track of total decoded frames elsewhere.
stat.fnum looks like what you need, or maybe xectx->decod_frames.

####################
DONE
--------------------
Removed
####################

> +        frame->format = AV_PIX_FMT_YUV420P10LE;

No need to set this here. ff_get_buffer() will handle it for you.
####################
DONE
-------------------- 
Removed
####################
> +
> +        if (ff_get_buffer(avctx, frame, 0) < 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get AV buffer\n");

ff_get_buffer() already prints an error, so remove this one.

> +            ret = AVERROR(ENOMEM);

It also returns an error code you should propagate.
####################
DONE
####################

> +            goto ERR;
> +        }
> +
> +        frame->pts = avpkt->pts;
> +
> +        av_image_copy(frame->data, frame->linesize, (const uint8_t **)imgb->a,
> +                      imgb->s, avctx->pix_fmt,
> +                      imgb->w[0], imgb->h[0]);
> +
> +        xectx->decod_frames++;

Write only variable.
####################
DONE
####################
> +        *got_frame_ptr = 1;
> +
> +        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    } else
> +        *got_frame_ptr = 0;
> +
> +    xectx->packet_count++;

Same.
####################
DONE
####################
> +
> +    return avpkt->size;
> +
> +ERR:
> +    if (imgb) {
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    }
> +    *got_frame_ptr = 0;
> +
> +    return ret;
> +}
> +
> +/**
> + * Destroy decoder
> + *
> + * @param avctx codec context
> + * @return 0 on success
> + */
> +static av_cold int libxevd_close(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    if (xectx->id) {
> +        xevd_delete(xectx->id);
> +        xectx->id = NULL;
> +    }
> +
> +    return 0;
> +}
> +
> +#define OFFSET(x) offsetof(XevdContext, x)
> +#define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
> +
> +static const AVClass libxevd_class = {
> +    .class_name = "libxevd",
> +    .item_name  = av_default_item_name,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> +const FFCodec ff_libxevd_decoder = {
> +    .p.name             = "evc",
> +    .p.long_name        = NULL_IF_CONFIG_SMALL("EVC / MPEG-5 Essential Video Coding (EVC)"),
> +    .p.type             = AVMEDIA_TYPE_VIDEO,
> +    .p.id               = AV_CODEC_ID_EVC,
> +    .init               = libxevd_init,
> +    FF_CODEC_DECODE_CB(libxevd_decode),
> +    .close              = libxevd_close,
> +    .priv_data_size     = sizeof(XevdContext),
> +    .p.priv_class       = &libxevd_class,
> +    .p.capabilities     = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AUTO_THREADS | AV_CODEC_CAP_AVOID_PROBING | AV_CODEC_CAP_DR1,

Use AV_CODEC_CAP_OTHER_THREADS, not AV_CODEC_CAP_AUTO_THREADS.
And set caps_internal to FF_CODEC_CAP_AUTO_THREADS.
####################
DONE
####################
> +    .p.wrapper_name     = "libxevd",
> +};

Hi James Almer,
Thank you for your last code review.
I did a lot of changes to our EVC wrapper implementation following your comments from the last code review and I'm looking forward to receiving your feedback.
We would like to start getting closer to the point where we can be able to merge our code into ffmpeg master branch. :)

Best regards 
Dawid

-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James Almer
Sent: Monday, August 1, 2022 5:09 PM
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/2] Provided support for MPEG-5 EVC (Essential Video Coding) codec

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/libxevd.c b/libavcodec/libxevd.c
> new file mode 100644
> index 0000000000..8ba2d89cbd
> --- /dev/null
> +++ b/libavcodec/libxevd.c
> @@ -0,0 +1,436 @@
> +/*
> + * libxevd decoder
> + * EVC (MPEG-5 Essential Video Coding) decoding using XEVD MPEG-5 EVC decoder library
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <float.h>
> +#include <stdlib.h>
> +
> +#include <xevd.h>
> +
> +#include "libavutil/internal.h"
> +#include "libavutil/common.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/pixdesc.h"
> +#include "libavutil/pixfmt.h"
> +#include "libavutil/imgutils.h"
> +#include "libavutil/cpu.h"
> +
> +#include "avcodec.h"
> +#include "internal.h"
> +#include "packet_internal.h"
> +#include "codec_internal.h"
> +
> +#define XEVD_PARAM_BAD_NAME -1
> +#define XEVD_PARAM_BAD_VALUE -2
> +
> +#define EVC_NAL_HEADER_SIZE 2 /* byte */
> +
> +/**
> + * The structure stores all the states associated with the instance of Xeve MPEG-5 EVC decoder
> + */
> +typedef struct XevdContext {
> +    const AVClass *class;
> +
> +    XEVD id;            // XEVD instance identifier @see xevd.h
> +    XEVD_CDSC cdsc;     // decoding parameters @see xevd.h
> +
> +    int decod_frames;   // number of decoded frames
> +    int packet_count;   // number of packets created by decoder
> +} XevdContext;
> +
> +/**
> + * The function returns a pointer to a variable of type XEVD_CDSC.

This doesn't seem to be the case.

> + * XEVD_CDSC contains all decoder parameters that should be initialized before its use.
> + *
> + * The field values of the XEVD_CDSC structure are populated based on:
> + * - the corresponding field values of the AvCodecConetxt structure,
> + * - the xevd decoder specific option values,
> + *   (the full list of options available for the xevd encoder is displayed after executing the command ./ffmpeg --help decoder = libxevd)
> + * - and the xevd encoder options specified as a list of key-value pairs following the xevd-params option
> + *
> + * Order of input processing and populating the XEVD_CDSC structure
> + * 1. first, the corresponding fields of the AVCodecContext structure are processed, (i.e -threads 4)
> + * 2. then xevd-specific options are added as AVOption to the xevd AVCodec implementation (i.e -threads 3)
> + * 3. finally, the options specified after the xevd-params option as the parameter list of type key value are processed (i.e -xevd-params "m=2")

I don't see a xevd-params option.

> + *
> + * Some options can be set in different ways. In this case, please follow the above-mentioned order of processing.
> + * The most recent assignments overwrite the previous values.
> + *
> + * @param[in] avctx codec context
> + * @param[out] cdsc contains all encoder parameters that should be initialized before its use
> + *
> + * @return 0 on success, negative error code on failure

I don't see a failure path below, so might as well just make this a void 
function.

> + */
> +static int get_conf(AVCodecContext *avctx, XEVD_CDSC *cdsc)
> +{
> +    int cpu_count = av_cpu_count();
> +
> +    /* clear XEVS_CDSC structure */
> +    memset(cdsc, 0, sizeof(XEVD_CDSC));
> +
> +    /* init XEVD_CDSC */
> +    if (avctx->thread_count <= 0)
> +        cdsc->threads = (cpu_count < XEVD_MAX_TASK_CNT) ? cpu_count : XEVD_MAX_TASK_CNT;
> +    else if (avctx->thread_count > XEVD_MAX_TASK_CNT)
> +        cdsc->threads = XEVD_MAX_TASK_CNT;
> +    else
> +        cdsc->threads = avctx->thread_count;
> +
> +    return 0;
> +}
> +
> +/**
> + * Read NAL unit length
> + * @param bs input data (bitstream)
> + * @return the length of NAL unit on success, 0 value on failure
> + */
> +static uint32_t read_nal_unit_length(const uint8_t *bs, int bs_size, AVCodecContext *avctx)
> +{
> +    uint32_t len = 0;
> +    XEVD_INFO info;
> +    int ret;
> +
> +    if (bs_size == XEVD_NAL_UNIT_LENGTH_BYTE) {
> +        ret = xevd_info((void *)bs, XEVD_NAL_UNIT_LENGTH_BYTE, 1, &info);
> +        if (XEVD_FAILED(ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information\n");
> +            return 0;
> +        }
> +        len = info.nalu_len;
> +        if (len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size! [%d]\n", bs_size);
> +            return 0;
> +        }
> +    }
> +
> +    return len;
> +}
> +
> +/**
> + * @param[in] xectx the structure that stores all the state associated with the instance of Xeve MPEG-5 EVC decoder
> + * @param[out] avctx codec context
> + * @return 0 on success, negative value on failure
> + */
> +static int export_stream_params(const XevdContext *xectx, AVCodecContext *avctx)
> +{
> +    int ret;
> +    int size;
> +    int color_space;
> +
> +    avctx->pix_fmt = AV_PIX_FMT_YUV420P10;
> +
> +    size = 4;
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_WIDTH, &avctx->coded_width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_HEIGHT, &avctx->coded_height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_WIDTH, &avctx->width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_HEIGHT, &avctx->height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_COLOR_SPACE, &color_space, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get color_space\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +    switch(color_space) {
> +    case XEVD_CS_YCBCR400_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +        break;
> +    case XEVD_CS_YCBCR420_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +        break;
> +    case XEVD_CS_YCBCR422_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +        break;
> +    case XEVD_CS_YCBCR444_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +        break;
> +    default:
> +        av_log(avctx, AV_LOG_ERROR, "Unknown color space\n");
> +        avctx->pix_fmt = AV_PIX_FMT_NONE;
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    // the function returns sps->num_reorder_pics
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_MAX_CODING_DELAY, &avctx->max_b_frames, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get max_coding_delay\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    avctx->has_b_frames = (avctx->max_b_frames) ? 1 : 0;
> +
> +    avctx->color_primaries = AVCOL_PRI_UNSPECIFIED;
> +    avctx->color_trc       = AVCOL_TRC_UNSPECIFIED;
> +    avctx->colorspace      = AVCOL_SPC_UNSPECIFIED;
> +
> +    return 0;
> +}
> +
> +/**
> + * Initialize decoder
> + * Create a decoder instance and allocate all the needed resources
> + *
> + * @param avctx codec context
> + * @return 0 on success, negative error code on failure
> + */
> +static av_cold int libxevd_init(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    int ret = 0;
> +    XEVD_CDSC *cdsc = &(xectx->cdsc);
> +
> +    /* read configurations and set values for created descriptor (XEVD_CDSC) */
> +    ret = get_conf(avctx, cdsc);
> +    if (ret != 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot get configuration\n");
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    /* create decoder */
> +    xectx->id = xevd_create(&(xectx->cdsc), NULL);
> +    if (xectx->id == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot create XEVD encoder\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    xectx->packet_count = 0;
> +    xectx->decod_frames = 0;
> +
> +    return 0;
> +}
> +
> +/**
> +  * Decode picture
> +  *
> +  * @param avctx codec context
> +  * @param[out] frame decoded frame
> +  * @param[out] got_frame_ptr decoder sets to 0 or 1 to indicate that a
> +  *                       non-empty frame or subtitle was returned in
> +  *                       outdata.
> +  * @param[in] avpkt AVPacket containing encoded data to be decoded
> +  *
> +  * @return amount of bytes read from the packet on success, negative error
> +  *         code on failure
> +  */
> +static int libxevd_decode(struct AVCodecContext *avctx, struct AVFrame *frame, int *got_frame_ptr, AVPacket *avpkt)
> +{
> +    XevdContext *xectx = NULL;
> +    XEVD_IMGB *imgb = NULL;
> +    XEVD_STAT stat;
> +    XEVD_BITB bitb;
> +    int xevd_ret, nalu_size, bs_read_pos;
> +    int ret = 0;
> +
> +    if (avctx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid input parameter: AVCodecContext\n");
> +        return AVERROR(EINVAL);
> +    }
> +    xectx = avctx->priv_data;
> +    if (xectx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid XEVD context\n");
> +        return AVERROR(EINVAL);

This can't happen, just remove the check.

> +    }
> +
> +    if (avpkt->size > 0) {
> +        bs_read_pos = 0;
> +        imgb = NULL;
> +        while(avpkt->size > (bs_read_pos + XEVD_NAL_UNIT_LENGTH_BYTE)) {
> +
> +            memset(&stat, 0, sizeof(XEVD_STAT));
> +            memset(&bitb, 0, sizeof(XEVD_BITB));
> +
> +            nalu_size = read_nal_unit_length(avpkt->data + bs_read_pos, XEVD_NAL_UNIT_LENGTH_BYTE, avctx);
> +            if (nalu_size == 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Invalid bitstream\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +            bs_read_pos += XEVD_NAL_UNIT_LENGTH_BYTE;
> +
> +            bitb.addr = avpkt->data + bs_read_pos;
> +            bitb.ssize = nalu_size;
> +
> +            /* main decoding block */
> +            xevd_ret = xevd_decode(xectx->id, &bitb, &stat);
> +            if (XEVD_FAILED(xevd_ret)) {
> +                av_log(avctx, AV_LOG_ERROR, "Failed to decode bitstream\n");
> +                ret = AVERROR_EXTERNAL;
> +                goto ERR;
> +            }
> +
> +            bs_read_pos += nalu_size;
> +
> +            if (stat.nalu_type == XEVD_NUT_SPS) { // EVC stream parameters changed
> +                if ((ret = export_stream_params(xectx, avctx)) != 0)
> +                    goto ERR;
> +            }
> +
> +            if (stat.read != nalu_size)
> +                av_log(avctx, AV_LOG_INFO, "Different reading of bitstream (in:%d,read:%d)\n,", nalu_size, stat.read);
> +            if (stat.fnum >= 0) {
> +                // already has a decoded image
> +                if (imgb) {
> +                    // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                    // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                    imgb->release(imgb);
> +                    imgb = NULL;
> +                }
> +                xevd_ret = xevd_pull(xectx->id, &imgb);
> +                if (XEVD_FAILED(xevd_ret)) {
> +                    av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d, frame#=%d)\n", xevd_ret, stat.fnum);
> +                    ret = AVERROR_EXTERNAL;
> +                    goto ERR;
> +                } else if (xevd_ret == XEVD_OK_FRM_DELAYED) {
> +                    if (imgb) {
> +                        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                        imgb->release(imgb);
> +                        imgb = NULL;
> +                    }
> +                }

So if the packet has more than one frame, you'll drop the oldest?

Maybe you should write this decoder using the decouple Input/Output API, 
FF_CODEC_RECEIVE_FRAME_CB() callback instead of FF_CODEC_DECODE_CB().
With it, you can request a packet as needed with ff_decode_get_packet(), 
so for example only when libxevd has run out of frames to output you 
actually request another.

> +            }
> +        }
> +    } else { // bumping
> +        xevd_ret = xevd_pull(xectx->id, &(imgb));
> +        if (xevd_ret == XEVD_ERR_UNEXPECTED) { // bumping process completed

Shouldn't this be XEVD_OK_NO_MORE_FRM?

> +            *got_frame_ptr = 0;
> +            return 0;
> +        } else if (XEVD_FAILED(xevd_ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d)\n", xevd_ret);
> +            ret = AVERROR_EXTERNAL;
> +            goto ERR;
> +        }
> +    }
> +
> +    if (imgb) {
> +        // @todo supports other color space and bit depth
> +        if (imgb->cs != XEVD_CS_YCBCR420_10LE) {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported pixel format: %s\n", av_get_pix_fmt_name(avctx->pix_fmt));
> +            ret = AVERROR_INVALIDDATA;
> +            goto ERR;
> +        }
> +
> +        if (imgb->w[0] != avctx->width || imgb->h[0] != avctx->height) { // stream resolution changed
> +            if (ff_set_dimensions(avctx, imgb->w[0], imgb->h[0]) < 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Cannot set new dimension\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +        }
> +
> +        frame->coded_picture_number++;
> +        frame->display_picture_number++;

As is, these two will always be 1. If you want to set these fields, you 
need to keep track of total decoded frames elsewhere.
stat.fnum looks like what you need, or maybe xectx->decod_frames.

> +        frame->format = AV_PIX_FMT_YUV420P10LE;

No need to set this here. ff_get_buffer() will handle it for you.

> +
> +        if (ff_get_buffer(avctx, frame, 0) < 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get AV buffer\n");

ff_get_buffer() already prints an error, so remove this one.

> +            ret = AVERROR(ENOMEM);

It also returns an error code you should propagate.

> +            goto ERR;
> +        }
> +
> +        frame->pts = avpkt->pts;
> +
> +        av_image_copy(frame->data, frame->linesize, (const uint8_t **)imgb->a,
> +                      imgb->s, avctx->pix_fmt,
> +                      imgb->w[0], imgb->h[0]);
> +
> +        xectx->decod_frames++;

Write only variable.

> +        *got_frame_ptr = 1;
> +
> +        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    } else
> +        *got_frame_ptr = 0;
> +
> +    xectx->packet_count++;

Same.

> +
> +    return avpkt->size;
> +
> +ERR:
> +    if (imgb) {
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    }
> +    *got_frame_ptr = 0;
> +
> +    return ret;
> +}
> +
> +/**
> + * Destroy decoder
> + *
> + * @param avctx codec context
> + * @return 0 on success
> + */
> +static av_cold int libxevd_close(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    if (xectx->id) {
> +        xevd_delete(xectx->id);
> +        xectx->id = NULL;
> +    }
> +
> +    return 0;
> +}
> +
> +#define OFFSET(x) offsetof(XevdContext, x)
> +#define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
> +
> +static const AVClass libxevd_class = {
> +    .class_name = "libxevd",
> +    .item_name  = av_default_item_name,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> +const FFCodec ff_libxevd_decoder = {
> +    .p.name             = "evc",
> +    .p.long_name        = NULL_IF_CONFIG_SMALL("EVC / MPEG-5 Essential Video Coding (EVC)"),
> +    .p.type             = AVMEDIA_TYPE_VIDEO,
> +    .p.id               = AV_CODEC_ID_EVC,
> +    .init               = libxevd_init,
> +    FF_CODEC_DECODE_CB(libxevd_decode),
> +    .close              = libxevd_close,
> +    .priv_data_size     = sizeof(XevdContext),
> +    .p.priv_class       = &libxevd_class,
> +    .p.capabilities     = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AUTO_THREADS | AV_CODEC_CAP_AVOID_PROBING | AV_CODEC_CAP_DR1,

Use AV_CODEC_CAP_OTHER_THREADS, not AV_CODEC_CAP_AUTO_THREADS.
And set caps_internal to FF_CODEC_CAP_AUTO_THREADS.

> +    .p.wrapper_name     = "libxevd",
> +};

Hi, 

Thank you for your code review and for all your valuable comments and remarks.
We have done a lot of changes to our EVC wrapper implementation following them, and I think each of these changes have moved our wrapper one step forwards toward a final community-acceptable solution. 
A few days ago I submitted new patches providing EVC wrapper implementation.
If there is still something we have to change or improve, please let me know.
I'm looking forward to receiving your feedback.

As I mentioned before we would like to start getting closer to the point where we can be able to merge our code into the FFmpeg master branch. :)

Once again, thank you for your effort and for supporting us and we are waiting for your feedback.

Best regards 
Dawid

-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James Almer
Sent: Monday, August 1, 2022 5:09 PM
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/2] Provided support for MPEG-5 EVC (Essential Video Coding) codec

On 8/1/2022 6:28 AM, Dawid Kozinski wrote:
> diff --git a/libavcodec/libxevd.c b/libavcodec/libxevd.c
> new file mode 100644
> index 0000000000..8ba2d89cbd
> --- /dev/null
> +++ b/libavcodec/libxevd.c
> @@ -0,0 +1,436 @@
> +/*
> + * libxevd decoder
> + * EVC (MPEG-5 Essential Video Coding) decoding using XEVD MPEG-5 EVC decoder library
> + *
> + * Copyright (C) 2021 Dawid Kozinski<d.kozinski@samsung.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <float.h>
> +#include <stdlib.h>
> +
> +#include <xevd.h>
> +
> +#include "libavutil/internal.h"
> +#include "libavutil/common.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/pixdesc.h"
> +#include "libavutil/pixfmt.h"
> +#include "libavutil/imgutils.h"
> +#include "libavutil/cpu.h"
> +
> +#include "avcodec.h"
> +#include "internal.h"
> +#include "packet_internal.h"
> +#include "codec_internal.h"
> +
> +#define XEVD_PARAM_BAD_NAME -1
> +#define XEVD_PARAM_BAD_VALUE -2
> +
> +#define EVC_NAL_HEADER_SIZE 2 /* byte */
> +
> +/**
> + * The structure stores all the states associated with the instance of Xeve MPEG-5 EVC decoder
> + */
> +typedef struct XevdContext {
> +    const AVClass *class;
> +
> +    XEVD id;            // XEVD instance identifier @see xevd.h
> +    XEVD_CDSC cdsc;     // decoding parameters @see xevd.h
> +
> +    int decod_frames;   // number of decoded frames
> +    int packet_count;   // number of packets created by decoder
> +} XevdContext;
> +
> +/**
> + * The function returns a pointer to a variable of type XEVD_CDSC.

This doesn't seem to be the case.

> + * XEVD_CDSC contains all decoder parameters that should be initialized before its use.
> + *
> + * The field values of the XEVD_CDSC structure are populated based on:
> + * - the corresponding field values of the AvCodecConetxt structure,
> + * - the xevd decoder specific option values,
> + *   (the full list of options available for the xevd encoder is displayed after executing the command ./ffmpeg --help decoder = libxevd)
> + * - and the xevd encoder options specified as a list of key-value pairs following the xevd-params option
> + *
> + * Order of input processing and populating the XEVD_CDSC structure
> + * 1. first, the corresponding fields of the AVCodecContext structure are processed, (i.e -threads 4)
> + * 2. then xevd-specific options are added as AVOption to the xevd AVCodec implementation (i.e -threads 3)
> + * 3. finally, the options specified after the xevd-params option as the parameter list of type key value are processed (i.e -xevd-params "m=2")

I don't see a xevd-params option.

> + *
> + * Some options can be set in different ways. In this case, please follow the above-mentioned order of processing.
> + * The most recent assignments overwrite the previous values.
> + *
> + * @param[in] avctx codec context
> + * @param[out] cdsc contains all encoder parameters that should be initialized before its use
> + *
> + * @return 0 on success, negative error code on failure

I don't see a failure path below, so might as well just make this a void 
function.

> + */
> +static int get_conf(AVCodecContext *avctx, XEVD_CDSC *cdsc)
> +{
> +    int cpu_count = av_cpu_count();
> +
> +    /* clear XEVS_CDSC structure */
> +    memset(cdsc, 0, sizeof(XEVD_CDSC));
> +
> +    /* init XEVD_CDSC */
> +    if (avctx->thread_count <= 0)
> +        cdsc->threads = (cpu_count < XEVD_MAX_TASK_CNT) ? cpu_count : XEVD_MAX_TASK_CNT;
> +    else if (avctx->thread_count > XEVD_MAX_TASK_CNT)
> +        cdsc->threads = XEVD_MAX_TASK_CNT;
> +    else
> +        cdsc->threads = avctx->thread_count;
> +
> +    return 0;
> +}
> +
> +/**
> + * Read NAL unit length
> + * @param bs input data (bitstream)
> + * @return the length of NAL unit on success, 0 value on failure
> + */
> +static uint32_t read_nal_unit_length(const uint8_t *bs, int bs_size, AVCodecContext *avctx)
> +{
> +    uint32_t len = 0;
> +    XEVD_INFO info;
> +    int ret;
> +
> +    if (bs_size == XEVD_NAL_UNIT_LENGTH_BYTE) {
> +        ret = xevd_info((void *)bs, XEVD_NAL_UNIT_LENGTH_BYTE, 1, &info);
> +        if (XEVD_FAILED(ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get bitstream information\n");
> +            return 0;
> +        }
> +        len = info.nalu_len;
> +        if (len == 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Invalid bitstream size! [%d]\n", bs_size);
> +            return 0;
> +        }
> +    }
> +
> +    return len;
> +}
> +
> +/**
> + * @param[in] xectx the structure that stores all the state associated with the instance of Xeve MPEG-5 EVC decoder
> + * @param[out] avctx codec context
> + * @return 0 on success, negative value on failure
> + */
> +static int export_stream_params(const XevdContext *xectx, AVCodecContext *avctx)
> +{
> +    int ret;
> +    int size;
> +    int color_space;
> +
> +    avctx->pix_fmt = AV_PIX_FMT_YUV420P10;
> +
> +    size = 4;
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_WIDTH, &avctx->coded_width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_CODED_HEIGHT, &avctx->coded_height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get coded_height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_WIDTH, &avctx->width, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get width\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_HEIGHT, &avctx->height, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get height\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_COLOR_SPACE, &color_space, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get color_space\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +    switch(color_space) {
> +    case XEVD_CS_YCBCR400_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_GRAY10LE;
> +        break;
> +    case XEVD_CS_YCBCR420_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
> +        break;
> +    case XEVD_CS_YCBCR422_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV422P10LE;
> +        break;
> +    case XEVD_CS_YCBCR444_10LE:
> +        avctx->pix_fmt = AV_PIX_FMT_YUV444P10LE;
> +        break;
> +    default:
> +        av_log(avctx, AV_LOG_ERROR, "Unknown color space\n");
> +        avctx->pix_fmt = AV_PIX_FMT_NONE;
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    // the function returns sps->num_reorder_pics
> +    ret = xevd_config(xectx->id, XEVD_CFG_GET_MAX_CODING_DELAY, &avctx->max_b_frames, &size);
> +    if (XEVD_FAILED(ret)) {
> +        av_log(avctx, AV_LOG_ERROR, "Failed to get max_coding_delay\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    avctx->has_b_frames = (avctx->max_b_frames) ? 1 : 0;
> +
> +    avctx->color_primaries = AVCOL_PRI_UNSPECIFIED;
> +    avctx->color_trc       = AVCOL_TRC_UNSPECIFIED;
> +    avctx->colorspace      = AVCOL_SPC_UNSPECIFIED;
> +
> +    return 0;
> +}
> +
> +/**
> + * Initialize decoder
> + * Create a decoder instance and allocate all the needed resources
> + *
> + * @param avctx codec context
> + * @return 0 on success, negative error code on failure
> + */
> +static av_cold int libxevd_init(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    int ret = 0;
> +    XEVD_CDSC *cdsc = &(xectx->cdsc);
> +
> +    /* read configurations and set values for created descriptor (XEVD_CDSC) */
> +    ret = get_conf(avctx, cdsc);
> +    if (ret != 0) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot get configuration\n");
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    /* create decoder */
> +    xectx->id = xevd_create(&(xectx->cdsc), NULL);
> +    if (xectx->id == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Cannot create XEVD encoder\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    xectx->packet_count = 0;
> +    xectx->decod_frames = 0;
> +
> +    return 0;
> +}
> +
> +/**
> +  * Decode picture
> +  *
> +  * @param avctx codec context
> +  * @param[out] frame decoded frame
> +  * @param[out] got_frame_ptr decoder sets to 0 or 1 to indicate that a
> +  *                       non-empty frame or subtitle was returned in
> +  *                       outdata.
> +  * @param[in] avpkt AVPacket containing encoded data to be decoded
> +  *
> +  * @return amount of bytes read from the packet on success, negative error
> +  *         code on failure
> +  */
> +static int libxevd_decode(struct AVCodecContext *avctx, struct AVFrame *frame, int *got_frame_ptr, AVPacket *avpkt)
> +{
> +    XevdContext *xectx = NULL;
> +    XEVD_IMGB *imgb = NULL;
> +    XEVD_STAT stat;
> +    XEVD_BITB bitb;
> +    int xevd_ret, nalu_size, bs_read_pos;
> +    int ret = 0;
> +
> +    if (avctx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid input parameter: AVCodecContext\n");
> +        return AVERROR(EINVAL);
> +    }
> +    xectx = avctx->priv_data;
> +    if (xectx == NULL) {
> +        av_log(avctx, AV_LOG_ERROR, "Invalid XEVD context\n");
> +        return AVERROR(EINVAL);

This can't happen, just remove the check.

> +    }
> +
> +    if (avpkt->size > 0) {
> +        bs_read_pos = 0;
> +        imgb = NULL;
> +        while(avpkt->size > (bs_read_pos + XEVD_NAL_UNIT_LENGTH_BYTE)) {
> +
> +            memset(&stat, 0, sizeof(XEVD_STAT));
> +            memset(&bitb, 0, sizeof(XEVD_BITB));
> +
> +            nalu_size = read_nal_unit_length(avpkt->data + bs_read_pos, XEVD_NAL_UNIT_LENGTH_BYTE, avctx);
> +            if (nalu_size == 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Invalid bitstream\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +            bs_read_pos += XEVD_NAL_UNIT_LENGTH_BYTE;
> +
> +            bitb.addr = avpkt->data + bs_read_pos;
> +            bitb.ssize = nalu_size;
> +
> +            /* main decoding block */
> +            xevd_ret = xevd_decode(xectx->id, &bitb, &stat);
> +            if (XEVD_FAILED(xevd_ret)) {
> +                av_log(avctx, AV_LOG_ERROR, "Failed to decode bitstream\n");
> +                ret = AVERROR_EXTERNAL;
> +                goto ERR;
> +            }
> +
> +            bs_read_pos += nalu_size;
> +
> +            if (stat.nalu_type == XEVD_NUT_SPS) { // EVC stream parameters changed
> +                if ((ret = export_stream_params(xectx, avctx)) != 0)
> +                    goto ERR;
> +            }
> +
> +            if (stat.read != nalu_size)
> +                av_log(avctx, AV_LOG_INFO, "Different reading of bitstream (in:%d,read:%d)\n,", nalu_size, stat.read);
> +            if (stat.fnum >= 0) {
> +                // already has a decoded image
> +                if (imgb) {
> +                    // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                    // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                    imgb->release(imgb);
> +                    imgb = NULL;
> +                }
> +                xevd_ret = xevd_pull(xectx->id, &imgb);
> +                if (XEVD_FAILED(xevd_ret)) {
> +                    av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d, frame#=%d)\n", xevd_ret, stat.fnum);
> +                    ret = AVERROR_EXTERNAL;
> +                    goto ERR;
> +                } else if (xevd_ret == XEVD_OK_FRM_DELAYED) {
> +                    if (imgb) {
> +                        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +                        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +                        imgb->release(imgb);
> +                        imgb = NULL;
> +                    }
> +                }

So if the packet has more than one frame, you'll drop the oldest?

Maybe you should write this decoder using the decouple Input/Output API, 
FF_CODEC_RECEIVE_FRAME_CB() callback instead of FF_CODEC_DECODE_CB().
With it, you can request a packet as needed with ff_decode_get_packet(), 
so for example only when libxevd has run out of frames to output you 
actually request another.

> +            }
> +        }
> +    } else { // bumping
> +        xevd_ret = xevd_pull(xectx->id, &(imgb));
> +        if (xevd_ret == XEVD_ERR_UNEXPECTED) { // bumping process completed

Shouldn't this be XEVD_OK_NO_MORE_FRM?

> +            *got_frame_ptr = 0;
> +            return 0;
> +        } else if (XEVD_FAILED(xevd_ret)) {
> +            av_log(avctx, AV_LOG_ERROR, "Failed to pull the decoded image (xevd error code: %d)\n", xevd_ret);
> +            ret = AVERROR_EXTERNAL;
> +            goto ERR;
> +        }
> +    }
> +
> +    if (imgb) {
> +        // @todo supports other color space and bit depth
> +        if (imgb->cs != XEVD_CS_YCBCR420_10LE) {
> +            av_log(avctx, AV_LOG_ERROR, "Not supported pixel format: %s\n", av_get_pix_fmt_name(avctx->pix_fmt));
> +            ret = AVERROR_INVALIDDATA;
> +            goto ERR;
> +        }
> +
> +        if (imgb->w[0] != avctx->width || imgb->h[0] != avctx->height) { // stream resolution changed
> +            if (ff_set_dimensions(avctx, imgb->w[0], imgb->h[0]) < 0) {
> +                av_log(avctx, AV_LOG_ERROR, "Cannot set new dimension\n");
> +                ret = AVERROR_INVALIDDATA;
> +                goto ERR;
> +            }
> +        }
> +
> +        frame->coded_picture_number++;
> +        frame->display_picture_number++;

As is, these two will always be 1. If you want to set these fields, you 
need to keep track of total decoded frames elsewhere.
stat.fnum looks like what you need, or maybe xectx->decod_frames.

> +        frame->format = AV_PIX_FMT_YUV420P10LE;

No need to set this here. ff_get_buffer() will handle it for you.

> +
> +        if (ff_get_buffer(avctx, frame, 0) < 0) {
> +            av_log(avctx, AV_LOG_ERROR, "Cannot get AV buffer\n");

ff_get_buffer() already prints an error, so remove this one.

> +            ret = AVERROR(ENOMEM);

It also returns an error code you should propagate.

> +            goto ERR;
> +        }
> +
> +        frame->pts = avpkt->pts;
> +
> +        av_image_copy(frame->data, frame->linesize, (const uint8_t **)imgb->a,
> +                      imgb->s, avctx->pix_fmt,
> +                      imgb->w[0], imgb->h[0]);
> +
> +        xectx->decod_frames++;

Write only variable.

> +        *got_frame_ptr = 1;
> +
> +        // xevd_pull uses pool of objects of type XEVD_IMGB.
> +        // The pool size is equal MAX_PB_SIZE (26), so release object when it is no more needed
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    } else
> +        *got_frame_ptr = 0;
> +
> +    xectx->packet_count++;

Same.

> +
> +    return avpkt->size;
> +
> +ERR:
> +    if (imgb) {
> +        imgb->release(imgb);
> +        imgb = NULL;
> +    }
> +    *got_frame_ptr = 0;
> +
> +    return ret;
> +}
> +
> +/**
> + * Destroy decoder
> + *
> + * @param avctx codec context
> + * @return 0 on success
> + */
> +static av_cold int libxevd_close(AVCodecContext *avctx)
> +{
> +    XevdContext *xectx = avctx->priv_data;
> +    if (xectx->id) {
> +        xevd_delete(xectx->id);
> +        xectx->id = NULL;
> +    }
> +
> +    return 0;
> +}
> +
> +#define OFFSET(x) offsetof(XevdContext, x)
> +#define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
> +
> +static const AVClass libxevd_class = {
> +    .class_name = "libxevd",
> +    .item_name  = av_default_item_name,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> +const FFCodec ff_libxevd_decoder = {
> +    .p.name             = "evc",
> +    .p.long_name        = NULL_IF_CONFIG_SMALL("EVC / MPEG-5 Essential Video Coding (EVC)"),
> +    .p.type             = AVMEDIA_TYPE_VIDEO,
> +    .p.id               = AV_CODEC_ID_EVC,
> +    .init               = libxevd_init,
> +    FF_CODEC_DECODE_CB(libxevd_decode),
> +    .close              = libxevd_close,
> +    .priv_data_size     = sizeof(XevdContext),
> +    .p.priv_class       = &libxevd_class,
> +    .p.capabilities     = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AUTO_THREADS | AV_CODEC_CAP_AVOID_PROBING | AV_CODEC_CAP_DR1,

Use AV_CODEC_CAP_OTHER_THREADS, not AV_CODEC_CAP_AUTO_THREADS.
And set caps_internal to FF_CODEC_CAP_AUTO_THREADS.

> +    .p.wrapper_name     = "libxevd",
> +};