// ranges: ranges in seconds
sS ffmpeg_makeSpliceFilter_multipleInputVideos(LL<DoubleRange> vids) {
  new LS out;
  int i = 0;
  for iVid over vids:
    fOr (DoubleRange r : vids.get(iVid)) {
      int lbl = ++i;
      S start = ffmpeg_formatSeconds(r.start);
      S end = ffmpeg_formatSeconds(r.end);
      out.add("[" + iVid + ":v]trim=start=" + start + ":end=" + end + ",setpts=PTS-STARTPTS[v" + lbl + "]");
      out.add("[" + iVid + ":a]atrim=start=" + start + ":end=" + end + ",asetpts=PTS-STARTPTS[a" + lbl + "]");
    }

  S concat = "concat=n=" + i;
  out.add(joinMap(iota(i), j -> "[v" + j + "]") + concat + "[outv]");
  out.add(joinMap(iota(i), j -> "[a" + j + "]") + + concat + ":v=0:a=1[outa]");
  ret joinWithSemicolon(out);
}

Began life as a copy of #1024579