vf_xfade softlocks filtergraph when crossfading different FPS video

[Stefan-Gabriel Muscalu]

Summary of the bug:

When cross-fading from a 60fps video to a 5fps video, xfade locks up and stops processing frames, but keeps the filtergraph locked

Version:

ffmpeg version 4.3.1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100

How to reproduce:

ffmpeg -f lavfi -i testsrc=r=60:d=5 -f lavfi -i testsrc=r=5:d=5 -filter_complex "
	[1:v] setpts=PTS-STARTPTS,settb=AVTB [v1];
	[0:v] setpts=PTS-STARTPTS,settb=AVTB [v0];
	[v0][v1] xfade=duration=0.5:transition=wipeleft:offset=4.5
" test.mp4 -y

Another example of such behavior is when cross-fading between a 60fps video and a 7fps video, but instead of locking the filter-graph, it ends the stream early, outputting a 5.8s video instead of a 9.5s video:

ffmpeg -f lavfi -i testsrc=r=60:d=5 -f lavfi -i testsrc=r=7:d=5 -filter_complex "
	[1:v] setpts=PTS-STARTPTS,settb=AVTB [v1];
	[0:v] setpts=PTS-STARTPTS,settb=AVTB [v0];
	[v0][v1] xfade=duration=0.5:transition=wipeleft:offset=4.5
" test.mp4 -y

[Stefan-Gabriel Muscalu]

Might be also related to ticket ​https://trac.ffmpeg.org/ticket/8823

[Elon Musk]

Both tickets are invalid, xfade works with only inputs that have same valid fps.

[Stefan-Gabriel Muscalu]

Ok, that invalidates this ticket, but 8823 is still valid as this example still reproduces it

ffmpeg -f lavfi -i testsrc=r=60:d=5 -f lavfi -i testsrc=r=60:d=5 -filter_complex "
	[1:v] setpts=PTS-STARTPTS,settb=AVTB,hue=90 [v1];
	[0:v] setpts=PTS-STARTPTS,settb=AVTB [v0];
	[v0][v1] xfade=duration=0.5:transition=wipeleft:offset=4.5
" test.mp4 -y

[Elon Musk]

Fixed in 4dbb75c437117285cfa195c437a8a1ee898e9293