The vlc.communicate("command") lines are sending commands directly to VLC media player, so they’re limited to what commands it actually supports.
I say “limited”, but there are quite a few more commands available in VLC than pHAT BEAT uses:
pi@raspberry:~ $ vlc -I rc
VLC media player 2.2.5 Weatherwax (revision 2.2.5-0-g9275f0fefa)
[0204da48] pulse audio output error: PulseAudio server connection failure: Connection refused
[02045630] core interface error: no suitable interface module
[01fae8f8] core libvlc error: interface "globalhotkeys,none" initialization failed
[01fce6c0] dbus interface error: Failed to connect to the D-Bus session daemon: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11
[01fce6c0] core interface error: no suitable interface module
[01fae8f8] core libvlc error: interface "dbus,none" initialization failed
[01fce608] [cli] lua interface: Listening on host "*console".
VLC media player 2.2.5 Weatherwax
Command Line Interface initialized. Type `help' for help.
longhelp
> +----[ CLI commands ]
| add XYZ . . . . . . . . . . . . . . . . . . . . add XYZ to playlist
| enqueue XYZ . . . . . . . . . . . . . . . . . queue XYZ to playlist
| playlist . . . . . . . . . . . . . show items currently in playlist
| search [string] . . search for items in playlist (or reset search)
| delete [X] . . . . . . . . . . . . . . . . delete item X in playlist
| move [X][Y] . . . . . . . . . . . . move item X in playlist after Y
| sort key . . . . . . . . . . . . . . . . . . . . . sort the playlist
| sd [sd] . . . . . . . . . . . . . show services discovery or toggle
| play . . . . . . . . . . . . . . . . . . . . . . . . . . play stream
| stop . . . . . . . . . . . . . . . . . . . . . . . . . . stop stream
| next . . . . . . . . . . . . . . . . . . . . . . next playlist item
| prev . . . . . . . . . . . . . . . . . . . . previous playlist item
| goto, gotoitem . . . . . . . . . . . . . . . . . goto item at index
| repeat [on|off] . . . . . . . . . . . . . . toggle playlist repeat
| loop [on|off] . . . . . . . . . . . . . . . . toggle playlist loop
| random [on|off] . . . . . . . . . . . . . . toggle playlist random
| clear . . . . . . . . . . . . . . . . . . . . . clear the playlist
| status . . . . . . . . . . . . . . . . . . . current playlist status
| title [X] . . . . . . . . . . . . . . set/get title in current item
| title_n . . . . . . . . . . . . . . . . next title in current item
| title_p . . . . . . . . . . . . . . previous title in current item
| chapter [X] . . . . . . . . . . . . set/get chapter in current item
| chapter_n . . . . . . . . . . . . . . next chapter in current item
| chapter_p . . . . . . . . . . . . previous chapter in current item
|
| seek X . . . . . . . . . . . seek in seconds, for instance `seek 12'
| pause . . . . . . . . . . . . . . . . . . . . . . . . toggle pause
| fastforward . . . . . . . . . . . . . . . . . . set to maximum rate
| rewind . . . . . . . . . . . . . . . . . . . . . set to minimum rate
| faster . . . . . . . . . . . . . . . . . . faster playing of stream
| slower . . . . . . . . . . . . . . . . . . slower playing of stream
| normal . . . . . . . . . . . . . . . . . . normal playing of stream
| rate [playback rate] . . . . . . . . . . set playback rate to value
| frame . . . . . . . . . . . . . . . . . . . . . play frame by frame
| fullscreen, f, F [on|off] . . . . . . . . . . . . toggle fullscreen
| info . . . . . . . . . . . . . information about the current stream
| stats . . . . . . . . . . . . . . . . show statistical information
| get_time . . . . . . . . . seconds elapsed since stream's beginning
| is_playing . . . . . . . . . . . . 1 if a stream plays, 0 otherwise
| get_title . . . . . . . . . . . . . the title of the current stream
| get_length . . . . . . . . . . . . the length of the current stream
|
| volume [X] . . . . . . . . . . . . . . . . . . set/get audio volume
| volup [X] . . . . . . . . . . . . . . . raise audio volume X steps
| voldown [X] . . . . . . . . . . . . . . lower audio volume X steps
| achan [X] . . . . . . . . . . . . set/get stereo audio output mode
| atrack [X] . . . . . . . . . . . . . . . . . . . set/get audio track
| vtrack [X] . . . . . . . . . . . . . . . . . . . set/get video track
| vratio [X] . . . . . . . . . . . . . . . set/get video aspect ratio
| vcrop, crop [X] . . . . . . . . . . . . . . . . set/get video crop
| vzoom, zoom [X] . . . . . . . . . . . . . . . . set/get video zoom
| vdeinterlace [X] . . . . . . . . . . . . . set/get video deinterlace
| vdeinterlace_mode [X] . . . . . . . set/get video deinterlace mode
| snapshot . . . . . . . . . . . . . . . . . . . . take video snapshot
| strack [X] . . . . . . . . . . . . . . . . . set/get subtitle track
| hotkey, key [hotkey name] . . . . . . . . . . simulate hotkey press
|
| vlm . . . . . . . . . . . . . . . . . . . . . . . . . load the VLM
| set [var [value]] . . . . . . . . . . . . . . . . . set/get env var
| save_env . . . . . . . . . . . . save env vars (for future clients)
| alias [cmd] . . . . . . . . . . . . . . . . set/get command aliases
| description . . . . . . . . . . . . . . . . . describe this module
| license . . . . . . . . . . . . . . . . print VLC's license message
| help, ? [pattern] . . . . . . . . . . . . . . . . . a help message
| longhelp [pattern] . . . . . . . . . . . . . . a longer help message
| lock . . . . . . . . . . . . . . . . . . . . lock the telnet prompt
| logout . . . . . . . . . . . . . . exit (if in a socket connection)
| quit . . . . . . . . quit VLC (or logout if in a socket connection)
| shutdown . . . . . . . . . . . . . . . . . . . . . . . shutdown VLC
+----[ end of help ]