Re: [FFmpeg-devel] [PATCH] avcodec/ituh263enc: Add AV_CODEC_CAP_SLICE_THREADS to old H.263

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> It is supported by the H.263+ AVCodec already
> 
> Is there any case where this does not work ?
> 
> Fixes regression of some command lines
> 
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/ituh263enc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libavcodec/ituh263enc.c b/libavcodec/ituh263enc.c
> index db7cdf1fcb..82dce05e36 100644
> --- a/libavcodec/ituh263enc.c
> +++ b/libavcodec/ituh263enc.c
> @@ -908,6 +908,7 @@ const FFCodec ff_h263_encoder = {
>      .p.id           = AV_CODEC_ID_H263,
>      .p.pix_fmts = (const enum AVPixelFormat[]){AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE},
>      .p.priv_class   = &h263_class,
> +    .p.capabilities = AV_CODEC_CAP_SLICE_THREADS,
>      .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE | FF_CODEC_CAP_INIT_CLEANUP,
>      .priv_data_size = sizeof(MpegEncContext),
>      .init           = ff_mpv_encode_init,

1. If you claim that there is a regression, you should mention the
commit that introduced them in the commit message (it's obviously
8ca4b515e73079cda068e253853654db394b8171 in this case).
2. What command lines regressed exactly? The only command lines that
should be affected by said commit are command lines that set the slices
option to a value > 1.
3. As the commit message of 8ca4b515e73079cda068e253853654db394b8171
explains, this was intentional, as the H.263 encoder produces broken
files with multiple slices (whether with slice-threading or not). One
gets all kinds of error messages when decoding such a file: "I cbpy
damaged at 1 7", "Error at MB: 316", "illegal ac vlc code at 0x29",
"slice end not reached but screenspace end (7 left 800000, score=
-125)", "run overflow at 0x7 i:1". Of course, there are visual
artifacts, too.
4. With this patch, this encoder will by default (at least, by the
defaults of the ffmpeg command line tool) produce broken files.
5. "Is there any case where this does not work ?": Is there any where it
works?

- Andreas
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