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

[Xiang, Haihao]

On Wed, 2021-06-09 at 16:03 +0000, Rogozhkin, Dmitry V wrote:
> 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?


Actually there is not a hang, but you have to wait for a long time to output the
frames. e.g. for a clip with 100 frames in my testing, there will be 4119956
frames to output.

[out_0_0 @ 0x55933fe3cd80] 100 buffers queued in out_0_0, something may be
wrong.
[out_0_0 @ 0x55933fe3cd80] 1000 buffers queued in out_0_0, something may be
wrong.
[out_0_0 @ 0x55933fe3cd80] 10000 buffers queued in out_0_0, something may be
wrong.
[out_0_0 @ 0x55933fe3cd80] 100000 buffers queued in out_0_0, something may be
wrong.
[out_0_0 @ 0x55933fe3cd80] 1000000 buffers queued in out_0_0, something may be
wrong.
frame=4119956 fps=509098 q=-0.0 Lsize=N/A time=38:08:51.96 bitrate=N/A
speed=1.7e+04x     
video:1770294kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknow



> 
> 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;