* add --unmute option to unmute the sound capture device if required,
  restoring the mute after finished capturing if it started muted.

* understand decoding errors when playing produced ogv files in
  mpv/ffmpeg:

  [ffmpeg/demuxer] ogg: Broken file, non-keyframe not correctly marked.
  [ffmpeg/demuxer] ogg: Broken file, keyframe not correctly marked.

* understand and correct video corruption artifacts, seems likely
  related to the above decoding errors.