Skipped frames when displaying RTP / H.264 stream

[jean-philippe]

Me again... I thought I'd post my latest findings in case it rings a bell
with anyone on the mailing list.

To recap, I detect one lost frame every 128 with the following pipeline:
videotestsrc is-live=true !
video/x-raw,width=640,height=480,format=I420,framerate=30/1 ! queue !
vpuenc_h264 ! queue ! rtph264pay ! queue ! rtph264depay ! fpsdisplaysink
text-overlay=false video-sink=fakesink sync=false

This is with the i.MX8MMini. So a 30Hz video stream comes out at 29.77Hz.

I've now found out that the H.264 stream contains one Filler NALU every 128
NALUs. 
The NALUs surrounding the Filler look fine, no different from the other VCL
NALUs in the stream.

So I think rtph264pay and/or rtph264depay may be dropping a frame when it
encounters a Filler NALU.

I'm now reading the RTP spec + looking at the code, but any suggestion
appreciated...



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