Ao usar "c0_mode" em vez de "all_mode", tudo bem.
ffplay -f lavfi "movie=left.mp4,setpts=PTS-STARTPTS,split[a1][a2];
movie=right.mp4,setpts=PTS-STARTPTS,split[b1][b2];
[a1][b1]blend=c0_mode=difference,pad=2*iw:ih:0:0[down];
[a2][b2]hstack[up];[up][down]vstack"
Umamaneiradecomparardoisvídeos.
ffplay-flavfi"movie=left.mp4,setpts=PTS-STARTPTS,split=3[a0][a1][a2];
movie=right.mp4,setpts=PTS-STARTPTS,split[b0][b1];
[a0][b0]blend=c0_mode=difference[y];
[a1]lutyuv=y=val:u=128:v=128[uv];
[y][uv]mergeplanes=0x001112:yuv420p,pad=2*iw:ih:0:0[down];
[a2][b1]hstack[up];[up][down]vstack"