[FFmpeg-devel] lead: support format 0x0

Fixes ticket #10660.
---

thanks to the mysterious 'ami_stuff'.

 libavcodec/leaddec.c | 38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

On Sun, Nov 12, 2023 at 11:41:23AM +1100, Peter Ross wrote:
> Fixes ticket #10660.
> ---
> 
> thanks to the mysterious 'ami_stuff'.
> 
>  libavcodec/leaddec.c | 38 ++++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/libavcodec/leaddec.c b/libavcodec/leaddec.c
> index fd2018256d..4f2cc03e65 100644
> --- a/libavcodec/leaddec.c
> +++ b/libavcodec/leaddec.c
> @@ -139,7 +139,7 @@ static int lead_decode_frame(AVCodecContext *avctx, AVFrame * frame,
>  {
>      LeadContext *s = avctx->priv_data;
>      const uint8_t * buf = avpkt->data;
> -    int ret, format, yuv20p_half = 0, fields = 1, q, size;
> +    int ret, format, yuv420p_div = 1, yuv20p_half = 0, fields = 1, q, size;
>      GetBitContext gb;
>      int16_t dc_pred[3] = {0, 0, 0};
>      uint16_t dequant[2][64];
> @@ -149,6 +149,10 @@ static int lead_decode_frame(AVCodecContext *avctx, AVFrame * frame,
>  
>      format = AV_RL16(buf + 4);
>      switch(format) {
> +    case 0x0:
> +        yuv420p_div = 2;
> +        avctx->pix_fmt = AV_PIX_FMT_YUV420P;
> +        break;
>      case 0x8000:
>          yuv20p_half = 1;
>          // fall-through
> @@ -192,29 +196,39 @@ static int lead_decode_frame(AVCodecContext *avctx, AVFrame * frame,
>      init_get_bits8(&gb, s->bitstream_buf, size);
>  
>      if (avctx->pix_fmt == AV_PIX_FMT_YUV420P) {
> -        for (int mb_y = 0; mb_y < (avctx->height + 15) / 16; mb_y++)
> +        for (int mb_y = 0; mb_y < (avctx->height + (16 / yuv420p_div - 1)) / (16 / yuv420p_div); mb_y++)
>              for (int mb_x = 0; mb_x < (avctx->width + 15) / 16; mb_x++)
> -                for (int b = 0; b < (yuv20p_half ? 4 : 6); b++) {
> -                    int luma_block = yuv20p_half ? 2 : 4;
> +                for (int b = 0; b < ((yuv420p_div == 2 || yuv20p_half) ? 4 : 6); b++) {
> +                    int luma_block = (yuv420p_div == 2 || yuv20p_half) ? 2 : 4;
>                      const VLCElem * dc_vlc = b < luma_block ? luma_dc_vlc.table : chroma_dc_vlc.table;
>                      int dc_bits            = b < luma_block ? LUMA_DC_BITS : CHROMA_DC_BITS;
>                      const VLCElem * ac_vlc = b < luma_block ? luma_ac_vlc.table : chroma_ac_vlc.table;
>                      int ac_bits            = b < luma_block ? LUMA_AC_BITS : CHROMA_AC_BITS;
> -                    int plane              = b < luma_block ? 0 : b - (yuv20p_half ? 1 : 3);
> -                    int x, y;
> +                    int plane              = b < luma_block ? 0 : b - (luma_block - 1);
> +                    int x, y, yclip;
>  
>                      if (b < luma_block) {
> -                        y = 16*mb_y + 8*(b >> 1);
> +                        y = (16 / yuv420p_div)*mb_y + 8*(b >> 1);
>                          x = 16*mb_x + 8*(b & 1);
> +                        yclip = 0;
>                      } else {
> -                        y = 8*mb_y;
> +                        y = (8 / yuv420p_div)*mb_y;
>                          x = 8*mb_x;
> +                        yclip = (yuv420p_div == 2) && y + 8 >= avctx->height / 2;
>                      }
>  
> -                    ret = decode_block(s, &gb, dc_vlc, dc_bits, ac_vlc, ac_bits,
> -                        dc_pred + plane, dequant[!(b < 4)],
> -                        frame->data[plane] + y*frame->linesize[plane] + x,
> -                        (yuv20p_half && b < 2 ? 2 : 1) * frame->linesize[plane]);
> +                    if (!yclip) {
> +                        ret = decode_block(s, &gb, dc_vlc, dc_bits, ac_vlc, ac_bits,
> +                            dc_pred + plane, dequant[!(b < 4)],
> +                            frame->data[plane] + y*frame->linesize[plane] + x,
> +                            (yuv20p_half && b < 2 ? 2 : 1) * frame->linesize[plane]);
> +                    } else {
> +                        uint8_t tmp[64];
> +                        ret = decode_block(s, &gb, dc_vlc, dc_bits, ac_vlc, ac_bits,
> +                            dc_pred + plane, dequant[!(b < 4)], tmp, 8);
> +                        for (int yy = 0; yy < 8 && y + yy < avctx->height / 2; yy++)
> +                            memcpy(frame->data[plane] + (y+yy)*frame->linesize[plane] + x, tmp + yy, 8);
> +                    }
>                      if (ret < 0)
>                          return ret;
>  

will apply in a few days.

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)