Expose all of the ffmpeg `amix` filters for the `--beep` option (6):
-b [true|false], --beep [true|false]
Beep instead of silence
-h <int>, --beep-hertz <int>
Beep frequency hertz (default: 1000)
--beep-mix-normalize [true|false]
Normalize mix of audio and beeps (default: True)
--beep-audio-weight <int>
Mix weight for non-beeped audio (default: 4)
--beep-sine-weight <int>
Mix weight for beep (default: 1)
--beep-dropout-transition <int>
Dropout transition for beep (default: 0)