liveMp4Arguments function

List<String> liveMp4Arguments(String input, String output, { required Duration length, String? chapters, })

The ffmpeg arguments that turn the recorder's input into an .mp4 at output: H.264 at a steady 60 fps, which editors and browsers play, with the chapters metadata file when there is one.

The video lasts exactly length, the time Metro recorded for. The iOS Simulator only writes a frame when the screen changes, and can give its last frame any length, so the last frame is held and then cut there.

Implementation

List<String> liveMp4Arguments(
  String input,
  String output, {
  required Duration length,
  String? chapters,
}) => [
  '-y',
  '-v',
  'error',
  '-i',
  input,
  if (chapters != null) ...['-i', chapters],
  '-map',
  '0:v:0',
  '-map',
  '0:a?',
  if (chapters != null) ...['-map_metadata', '1', '-map_chapters', '1'],
  '-vf',
  '${_holdLastFrame(length)},fps=60,scale=trunc(iw/2)*2:trunc(ih/2)*2',
  '-c:v',
  'libx264',
  '-preset',
  'veryfast',
  '-crf',
  '20',
  '-pix_fmt',
  'yuv420p',
  '-c:a',
  'aac',
  '-movflags',
  '+faststart',
  '-t',
  _seconds(length),
  output,
];