To be investigated issues
With threads >= 1 and libav
MTS regression (worked-around)
Possibly VLC TS demuxer does not output correct IDR information.
Whether the demuxer is wrong or not, it fails with libav, but it works with FFmpeg.
Some VC1i sample did not work in libav: http://streams.videolan.org/issues/5887/Journey%20to%20the%20Edge%20of%20the%20Universe%20sample.mkv
FFv1 v1.3 support
Lagarith YV12 direct-rendering
YV12 broken in libav when using direct-rendering. Numerous reports about that. https://forum.videolan.org/viewtopic.php?f=14&t=115983&hilit=lagarith
XVid "Bulletproof's Heavy Compression Matrix" fails in libav, works in FFmpeg.
VLC fails to play on non-SSE2 machines in libav
See the bugreport here https://trac.videolan.org/vlc/ticket/10203 and see the numerous complaints on the forum here https://forum.videolan.org/viewtopic.php?f=2&t=115952&p=393815&hilit=athlon#p393815
With FFmpeg, HuffYUv is broken. See https://trac.ffmpeg.org/ticket/3395
MXF playback broken - part 1
No video on this 1080p50 sample in libav: http://streams.videolan.org/misc/mxf/1080p50.MXF
MXF playback broken - part 2
No seek after 4GB on this sample in libav http://streams.videolan.org/misc/mxf.zip