ffmpeg video mixing

Lessons for mixing video clips with ffmpeg while keeping audio and video in sync.

problem: audio/video desync when mixing clips

what went wrong

using -ss X -t Y to pre-trim input, then applying relative trim filters caused timing drift:

# BAD: relative timestamps after pre-trim
ffmpeg -ss 64 -t 36 -i original.mp4 ...
  -filter_complex "
    [0:v]split=5[orig1][orig2]...;
    [orig1]trim=0:4,setpts=PTS-STARTPTS[o1];
    [orig2]trim=4:11,setpts=PTS-STARTPTS[o2];
    ..."