Here's one that generates AppStore previews with correct sizes and metadata. (iTunes Connect can be really picky about this sometimes.)

  # 1. Record your device using QuickTime 
  #  (File->New Movie Recording->Select your phone)
  # 2. Run `$ app-preview your-recording.mov`

  function app-preview() {
      echo "name $1"
      ffmpeg -i $1 -vf scale=1080:1920,setsar=1 -c:a copy "out_$1"
  }