Moves the two Volume sliders (volumes.song and volumes.original, each 0 to 100).
Nothing is sent. Answers the same editor with the new levels; the Reel's Share mixes the
song and the original at them.
Taps Done: the song is saved to the recent audio and the music sheet closes back to the Reel editor. Answers the song.
The actions of PostingReelMusicEditorScreen: the methods you call on its handle while the screen is open.