Re: [FFmpeg-devel] [PATCH 1/3] avcodec/vp8: Enforce key-frame only for WebP

[Thilo Borgmann via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

On 03.02.24 14:57, Andreas Rheinhardt wrote:
> Andreas Rheinhardt:
>> VP8-in-WebP only uses key frame encoding (see [1]), yet this
>> is currently not enforced. This commit does so in order to
>> make output reproducible with frame-threading as the VP8 decoder's
>> update_thread_context is not called at all when using decoding
>> VP8-in-WebP (as this is unnecessary for key frame-only streams).
>>
>> [1]: https://developers.google.com/speed/webp/docs/riff_container
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>> ---
>>   libavcodec/vp8.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c
>> index 83c60adeb0..7972775a1c 100644
>> --- a/libavcodec/vp8.c
>> +++ b/libavcodec/vp8.c
>> @@ -2665,7 +2665,11 @@ int vp78_decode_frame(AVCodecContext *avctx, AVFrame *rframe, int *got_frame,
>>       if (ret < 0)
>>           goto err;
>>   
>> -    if (s->actually_webp) {
>> +    if (!is_vp7 && s->actually_webp) {
>> +        // VP8 in WebP is supposed to be intra-only. Enforce this here
>> +        // to ensure that output is reproducible with frame-threading.
>> +        if (!s->keyframe)
>> +            return AVERROR_INVALIDDATA;
>>           // avctx->pix_fmt already set in caller.
>>       } else if (!is_vp7 && s->pix_fmt == AV_PIX_FMT_NONE) {
>>           s->pix_fmt = get_pixel_format(s);
> 
> Will apply this patchset tomorrow unless there are objections.

Works as expected for me for a coupled version of the animated webp 
decoder which can follow-up.

Thanks,
Thilo
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