[FFmpeg-devel] [PATCH 2/2] lavfi/vf_vpp_qsv: fix the time_base for outlink

[Rogozhkin, Dmitry V]

On Wed, 2021-06-09 at 12:18 +0800, Haihao Xiang wrote:
> Since commit 89ffcd1, the pts on output pad is in the time base of
> the
> input link, not the time base of the output link when EOF is reached,
> so
> a filter after vpp_qsv might output some unexpected frames. In order
> to
> avoid this issue, use the same time base for input and ouput links

I believe this is partially misleading description since it is not
clearly describing application behavior. Impression might be that below
console error messages and some unexpected frames is the only
consequence. But it is not. In fact, application hangs in the very end
of the processing. Secondly, it is not clear what unexpected frames
results to? will there be more frames than should be in the final
bitstream or less?

Can you, please, polish commit message clarifying how exactly
application could misbehave? Pay attention on the hang, please.

Also, please, refer https://trac.ffmpeg.org/ticket/9286 which I
submitted for this issue. I verified that these 2 patches fix the
issue, but I am not sure which patch exactly fixed app hang.

> 
> The issue can be triggered with the command below:
> $> ffmpeg -hwaccel qsv -c:v hevc_qsv -i input.h265 -vf
> "vpp_qsv=w=1920:h=1080,fps=fps=60" -f null -
> 
> [out_0_0 @ 0x55eb017b5060] 100 buffers queued in out_0_0, something
> may
> be wrong.
> [out_0_0 @ 0x55eb017b5060] 1000 buffers queued in out_0_0, something
> may
> be wrong.
> [out_0_0 @ 0x55eb017b5060] 10000 buffers queued in out_0_0, something
> may be wrong.
> ---
>  libavfilter/vf_vpp_qsv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavfilter/vf_vpp_qsv.c b/libavfilter/vf_vpp_qsv.c
> index b9ab5c6490..74d1d51e7c 100644
> --- a/libavfilter/vf_vpp_qsv.c
> +++ b/libavfilter/vf_vpp_qsv.c
> @@ -303,7 +303,7 @@ static int config_output(AVFilterLink *outlink)
>      outlink->w          = vpp->out_width;
>      outlink->h          = vpp->out_height;
>      outlink->frame_rate = vpp->framerate;
> -    outlink->time_base  = av_inv_q(vpp->framerate);
> +    outlink->time_base  = inlink->time_base;
>  
>      param.filter_frame  = NULL;
>      param.num_ext_buf   = 0;