sS ffmpeg_makeSpliceFilter(L<DoubleRange> ranges) {
  ret "[0:v]trim=start=1:end=5,setpts=PTS-STARTPTS[av]; \
    [0:a]atrim=start=1:end=5,asetpts=PTS-STARTPTS[aa];\
    [0:v]trim=start=20:end=23.5,setpts=PTS-STARTPTS[bv]; \
    [0:a]atrim=start=20:end=23.5,asetpts=PTS-STARTPTS[ba];\
    [av][bv]concat[outv]; [aa][ba]concat=v=0:a=1[outa]";
}