[mythtv] FFmpeg 4.4.1 problems

[Peter Bennett]

David

I saw your commit for reducing prebuffer.

I am trying to get ffmpeg 4.4.1 in shape in the devel/ffmpeg-resync 
branch. Klaas has reported picture corruption which sometimes happens at 
start of play or after a jump and lasts up to 2 seconds. This happens 
with VDPAU on interlaced H264 videos. Also to a lesser extent with NVDEC 
on interlaced H264 videos (only lasts a small fraction of a second with 
NVDEC as far as I have seen). it only happens on about one out of ten 
jumps on VDPAU.

The workaround I am looking at is to "prime" the decoder with an extra 2 
seconds of data that are not shown, so that the first picture seen will 
not be corrupted. This would cause a small delay after a jump, which may 
be unacceptable, or may be less acceptable that seeing a couple of 
seconds of corruption. I don't know if this is a good workaround.

For fast forward or rewind this would not make sense so it would have to 
be suppressed.

Let me know if anybody has any suggestions, better ideas, etc.

Peter