[FFmpeg-devel] [PATCH] mjpegdec: Support 4x1, 2x1, 2x1 notation for 4:2:2 chroma subsampling

[Michael Niedermayer]

On Mon, Jun 18, 2018 at 09:19:30PM +0100, Derek Buitenhuis wrote:
> Just one of the many, many ways to store this stuff in the header.
> 
> Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
> ---
> Related reading, but not exactly the same type:
>     * https://github.com/libjpeg-turbo/libjpeg-turbo/issues/92
>     * https://github.com/libjpeg-turbo/libjpeg-turbo/commit/8ce2c9119a995ef6280f8bba375aac7effb9b571
> ---
>  libavcodec/mjpegdec.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
> index d1dca84d36..e5888ed548 100644
> --- a/libavcodec/mjpegdec.c
> +++ b/libavcodec/mjpegdec.c
> @@ -568,6 +568,7 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
>          }
>          break;
>      case 0x21111100:
> +    case 0x41212100:
>          if (s->component_id[0] == 'Q' && s->component_id[1] == 'F' && s->component_id[2] == 'A') {
>              if (s->bits <= 8) s->avctx->pix_fmt = AV_PIX_FMT_GBRP;
>              else

either this is wrong or
"
 -    /* NOTE we do not allocate pictures large enough for the possible
 -     * padding of h/v_count being 4 */
 "
this is outdated in some way.

in fact we do at least in mjpeg_decode_scan() check w/h and skip writing
outside. So this may be ok but then it would be simpler
to update 
     if (!(pix_fmt_id & 0xD0D0D0D0))
         pix_fmt_id -= (pix_fmt_id & 0xF0F0F0F0) >> 1;
     if (!(pix_fmt_id & 0x0D0D0D0D))
         pix_fmt_id -= (pix_fmt_id & 0x0F0F0F0F) >> 1;

to also work with the count=4 cases

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
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