Debugging video jerking problem

[Nicolas Dufresne]

Le jeudi 06 décembre 2018 à 14:59 +0100, Wolfgang Grandegger a écrit :
> Hello,
> 
> I'm currently debugging a jerking problem. When I move from 50 to 60
> FPS, the displayed video starts jerking. Just a little bit but it's
> clearly visible when the camera pans. Here is my pipeline:
> 
>          gst-launch-1.0 -v \
>           udpsrc port=50004 buffer-size=180000000 do-timestamp=1 \
>             caps="application/x-rtp, media=(string)video, clock-rate=(int)90000, \
>             encoding-name=(string)JPEG, payload=(int)26, framerate=(fraction)60/1" \
>           ! rtpjitterbuffer latency=20 \
>           ! rtpjpegdepay \
>           ! vaapijpegdec \
>           ! timeoverlay text="A Text ..."
>           ! tee name=t
>           t. ! queue ! vaapisink
>           t. ! queue ! vaapih264enc ! mp4mux ! filesink location=/tmp/test.mp4
> 
> I have connected a signal for under- and overruns to both, the display and
> record queue. What I see when the jerking starts is that I get underruns
> on the display (vaapisink) queue. Does that mean that the packets do not
> arrive in time due to pre-processing time? The jerking goes away if I remove
> the tee for recording or run the video at just 50 FPS.
> Any ideas what could cause the jerking and how it can be debugged or even
> avoided?

My guess would be that when going for 60 to 50 FPS you increase the
latency. This is because H264 decoding latency is in number of frames.
So the longer the duration of a frame, the longer he latency. Ideally,
you would through your RTP signalling make the caps changes when the
FPS changes so that latency can be recalculated. You can also use
pipeline latency, or processing-latency on sinks.

> 
> Any help is appreciated.
> 
> Thanks,
> 
> Wolfgang.
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