[FFmpeg-devel] [PATCH] avcodec/decode: Return EAGAIN instead of overwriting unused packet

[Anton Khirnov]

Quoting Andreas Rheinhardt (2023-07-10 01:36:41)
> Should fix #10457, a regression caused by
> 69516ab3e917a6e91d26e38d04183c60fd71cbab.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
> I am not sure about this one. The problem is that avcodec_send_packet()
> and avcodec_receive_frame() must not return EAGAIN at the same time.
> If buffer_frame contains a frame when entering avcodec_send_packet(),
> the next call to avcodec_receive_frame() will not return EAGAIN.
> But is this actually guaranteed if buffer_pkt is not empty?

It's not guaranteed, but I believe the correct interpretation of the
"must not return EAGAIN at the same time" line is that
send->receive->send must make progress and not be 3x EAGAIN.


> 
>  libavcodec/decode.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index 269633ce10..6595c3ca34 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -666,6 +666,9 @@ int attribute_align_arg avcodec_send_packet(AVCodecContext *avctx, const AVPacke
>      if (avpkt && !avpkt->size && avpkt->data)
>          return AVERROR(EINVAL);
>  
> +    if (!AVPACKET_IS_EMPTY(avci->buffer_pkt))
> +        return AVERROR(EAGAIN);
> +
>      av_packet_unref(avci->buffer_pkt);

This unref here becomes redundant.

Otherwise looks good, thanks.

-- 
Anton Khirnov