[FFmpeg-devel,5/8] lavc/encode: add an encoder-specific get_buffer() variant

Several encoders (roqvideo, svq1, snow, and the mpegvideo family)
currently call ff_get_buffer(). However this function is written
assuming it is called by a decoder. Though nothing has been obviously
broken by this until now, this may change in the future.

To avoid potential future issues, introduce a simple encode-specific
wrapper around avcodec_default_get_buffer2() and enforce its use in
encoders.
---
 libavcodec/decode.c      |  2 ++
 libavcodec/encode.c      | 34 ++++++++++++++++++++++++++++++++++
 libavcodec/encode.h      |  5 +++++
 libavcodec/mpegpicture.c | 16 +++++++++-------
 libavcodec/roqvideoenc.c |  4 ++--
 libavcodec/snow.c        |  8 ++++++--
 libavcodec/svq1enc.c     |  4 ++--
 7 files changed, 60 insertions(+), 13 deletions(-)

On 3/23/2022 12:57 PM, Anton Khirnov wrote:
> Several encoders (roqvideo, svq1, snow, and the mpegvideo family)
> currently call ff_get_buffer(). However this function is written
> assuming it is called by a decoder. Though nothing has been obviously
> broken by this until now, this may change in the future.
> 
> To avoid potential future issues, introduce a simple encode-specific
> wrapper around avcodec_default_get_buffer2() and enforce its use in
> encoders.
> ---
>   libavcodec/decode.c      |  2 ++
>   libavcodec/encode.c      | 34 ++++++++++++++++++++++++++++++++++
>   libavcodec/encode.h      |  5 +++++
>   libavcodec/mpegpicture.c | 16 +++++++++-------
>   libavcodec/roqvideoenc.c |  4 ++--
>   libavcodec/snow.c        |  8 ++++++--
>   libavcodec/svq1enc.c     |  4 ++--
>   7 files changed, 60 insertions(+), 13 deletions(-)
> 
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index fffad5f700..3733e6d4b8 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -1405,6 +1405,8 @@ int ff_get_buffer(AVCodecContext *avctx, AVFrame *frame, int flags)
>       int override_dimensions = 1;
>       int ret;
>   
> +    av_assert0(av_codec_is_decoder(avctx->codec));
> +
>       if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
>           if ((unsigned)avctx->width > INT_MAX - STRIDE_ALIGN ||
>               (ret = av_image_check_size2(FFALIGN(avctx->width, STRIDE_ALIGN), avctx->height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx)) < 0 || avctx->pix_fmt<0) {
> diff --git a/libavcodec/encode.c b/libavcodec/encode.c
> index 837ffaa40d..ec8d06d068 100644
> --- a/libavcodec/encode.c
> +++ b/libavcodec/encode.c
> @@ -572,3 +572,37 @@ FF_ENABLE_DEPRECATION_WARNINGS
>   
>       return 0;
>   }
> +
> +int ff_encode_alloc_frame(AVCodecContext *avctx, AVFrame *frame)
> +{
> +    int ret;
> +
> +    switch (avctx->codec->type) {
> +    case AVMEDIA_TYPE_VIDEO:
> +        frame->format = avctx->pix_fmt;
> +        if (frame->width <= 0 || frame->height <= 0) {
> +            frame->width  = FFMAX(avctx->width,  avctx->coded_width);
> +            frame->height = FFMAX(avctx->height, avctx->coded_height);
> +        }
> +
> +        break;
> +    case AVMEDIA_TYPE_AUDIO:
> +        frame->sample_rate = avctx->sample_rate;
> +        frame->format      = avctx->sample_fmt;
> +        if (!frame->ch_layout.nb_channels) {
> +            int ret = av_channel_layout_copy(&frame->ch_layout, &avctx->ch_layout);

Unnecessarily shadowing ret.

> +            if (ret < 0)
> +                return ret;
> +        }
> +        break;
> +    }
> +
> +    ret = avcodec_default_get_buffer2(avctx, frame, 0);
> +    if (ret < 0) {
> +        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
> +        av_frame_unref(frame);
> +        return ret;
> +    }
> +
> +    return 0;
> +}
> diff --git a/libavcodec/encode.h b/libavcodec/encode.h
> index 97b3acf9df..b2536bf0f3 100644
> --- a/libavcodec/encode.h
> +++ b/libavcodec/encode.h
> @@ -44,6 +44,11 @@ int ff_encode_get_frame(AVCodecContext *avctx, AVFrame *frame);
>    */
>   int ff_get_encode_buffer(AVCodecContext *avctx, AVPacket *avpkt, int64_t size, int flags);
>   
> +/**
> + * Allocate buffers for a frame. Encoder equivalent to ff_get_buffer().
> + */
> +int ff_encode_alloc_frame(AVCodecContext *avctx, AVFrame *frame);
> +
>   /**
>    * Check AVPacket size and allocate data.
>    *
> diff --git a/libavcodec/mpegpicture.c b/libavcodec/mpegpicture.c
> index 681ccc2b82..aaa1df0bd8 100644
> --- a/libavcodec/mpegpicture.c
> +++ b/libavcodec/mpegpicture.c
> @@ -26,6 +26,7 @@
>   #include "libavutil/imgutils.h"
>   
>   #include "avcodec.h"
> +#include "encode.h"
>   #include "motion_est.h"
>   #include "mpegpicture.h"
>   #include "mpegutils.h"
> @@ -123,14 +124,15 @@ static int alloc_frame_buffer(AVCodecContext *avctx,  Picture *pic,
>       int r, ret;
>   
>       pic->tf.f = pic->f;
> -    if (avctx->codec_id != AV_CODEC_ID_WMV3IMAGE &&
> -        avctx->codec_id != AV_CODEC_ID_VC1IMAGE  &&
> -        avctx->codec_id != AV_CODEC_ID_MSS2) {
> -        if (edges_needed) {
> -            pic->f->width  = avctx->width  + 2 * EDGE_WIDTH;
> -            pic->f->height = avctx->height + 2 * EDGE_WIDTH;
> -        }
>   
> +    if (edges_needed) {
> +        pic->f->width  = avctx->width  + 2 * EDGE_WIDTH;
> +        pic->f->height = avctx->height + 2 * EDGE_WIDTH;
> +
> +        r = ff_encode_alloc_frame(avctx, pic->f);
> +    } else if (avctx->codec_id != AV_CODEC_ID_WMV3IMAGE &&
> +               avctx->codec_id != AV_CODEC_ID_VC1IMAGE  &&
> +               avctx->codec_id != AV_CODEC_ID_MSS2) {
>           r = ff_thread_get_ext_buffer(avctx, &pic->tf,
>                                        pic->reference ? AV_GET_BUFFER_FLAG_REF : 0);
>       } else {
> diff --git a/libavcodec/roqvideoenc.c b/libavcodec/roqvideoenc.c
> index ef7861088d..95db514140 100644
> --- a/libavcodec/roqvideoenc.c
> +++ b/libavcodec/roqvideoenc.c
> @@ -1081,8 +1081,8 @@ static int roq_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
>       if (enc->first_frame) {
>           /* Alloc memory for the reconstruction data (we must know the stride
>            for that) */
> -        if ((ret = ff_get_buffer(avctx, roq->current_frame, 0)) < 0 ||
> -            (ret = ff_get_buffer(avctx, roq->last_frame,    0)) < 0)
> +        if ((ret = ff_encode_alloc_frame(avctx, roq->current_frame)) < 0 ||
> +            (ret = ff_encode_alloc_frame(avctx, roq->last_frame   )) < 0)
>               return ret;
>   
>           /* Before the first video frame, write a "video info" chunk */
> diff --git a/libavcodec/snow.c b/libavcodec/snow.c
> index 1224b95491..bc0d9a8983 100644
> --- a/libavcodec/snow.c
> +++ b/libavcodec/snow.c
> @@ -23,6 +23,7 @@
>   #include "libavutil/opt.h"
>   #include "libavutil/thread.h"
>   #include "avcodec.h"
> +#include "encode.h"
>   #include "me_cmp.h"
>   #include "snow_dwt.h"
>   #include "internal.h"
> @@ -76,8 +77,11 @@ int ff_snow_get_buffer(SnowContext *s, AVFrame *frame)
>       if (edges_needed) {
>           frame->width  += 2 * EDGE_WIDTH;
>           frame->height += 2 * EDGE_WIDTH;
> -    }
> -    if ((ret = ff_get_buffer(s->avctx, frame, AV_GET_BUFFER_FLAG_REF)) < 0)
> +
> +        ret = ff_encode_alloc_frame(s->avctx, frame);
> +    } else
> +        ret = ff_get_buffer(s->avctx, frame, AV_GET_BUFFER_FLAG_REF);
> +    if (ret < 0)
>           return ret;
>       if (edges_needed) {
>           for (i = 0; frame->data[i]; i++) {
> diff --git a/libavcodec/svq1enc.c b/libavcodec/svq1enc.c
> index 706bc2e42e..cb0d0308fc 100644
> --- a/libavcodec/svq1enc.c
> +++ b/libavcodec/svq1enc.c
> @@ -595,12 +595,12 @@ static int svq1_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
>       }
>   
>       if (!s->current_picture->data[0]) {
> -        if ((ret = ff_get_buffer(avctx, s->current_picture, 0)) < 0) {
> +        if ((ret = ff_encode_alloc_frame(avctx, s->current_picture)) < 0) {
>               return ret;
>           }
>       }
>       if (!s->last_picture->data[0]) {
> -        ret = ff_get_buffer(avctx, s->last_picture, 0);
> +        ret = ff_encode_alloc_frame(avctx, s->last_picture);
>           if (ret < 0)
>               return ret;
>       }