Even though Mastering Music Online is running in the browser, you can connect a keyboard and record MIDI in real-time.
After keyboard connection, open Mastering Music Online and set the MIDI driver on the desired tracks, set the metronome
to the correct driver, set the record mode (overdub or replace), set the tempo then click record and play. The played
performance will be recorded. There is no limit on the number of tracks that can be recorded in this manner so for
those with keyboard skills you can very quickly build up a new song consisting of multiple tracks/instruments.