SPACE - Begin playback (During playback: Enter Pausemode/Leave Pausemode)
ENTER/RETURN - Begin playback (During playback: Stop playing)
LEFT ARROW - Jump to next item in playlist
RIGHT ARROW - Jump to previous item in playlist
UP/DOWN ARROW - Move highlight bar up/down in playlist
TAB - Deselect any highlighted items in playlist
KEYS 0-7 - Set mastervolume

Cmd+N - New playlist
Cmd+O - Open playlist
Cmd+S - Save playlist
Cmd+Q - Quit MPLAY
Cmd+F - Enter Audio fullscreen (only during audio playback)
Cmd+M - Switch between minimized mode/normal mode
Cmd+R - Toggles Random playback on/off
Cmd+L - Toggles Looped playback on/off
Cmd+T - Open/close the Track Mixer
Cmd+, - Brings up the Sorting Window for sorting the playlist in different ways
Cmd++ - Increase mastervolume (Cmd+= on US keyboards)
Cmd+- - Decrease mastervolume
Cmd+P - Open/close the Preferences window
Cmd+H - Opens the QuickReference (the one you're reading!) if it resides in the Tools-folder
Cmd+I - Open the built-in ID3 Tag Editor (Note: only available when a MP3-file is selected and during non-playback)
Cmd+E - Ejects the CD-tray for loading/unloading CD's (Note: only selectable during non-playback)
Cmd+A - Add all MPEG-tracks from valid VideoCD (Note: only selectable during non-playback)