Another way to play a MIDI file is by connecting a MIDI player to MPP's MIDI input through a virtual loopback MIDI port. This method is far more robust and efficient; you can do a lot of things with the MIDI I/O. It also works with World of Pixels Piano, PianoRhythm, and any other program that has a MIDI input.
You will need:
• A MIDI player program that can output MIDI, such as Synthesia, MIDITrail, or Piano From Above
• A virtual MIDI port
• A web browser that supports WebMIDI, such as Google Chrome or most Chromium derivates (Opera, Vivaldi, etc).
Note that most other browsers (Firefox, Safari, Edge, IE, etc) do not support WebMIDI and the MIDI In/Out button will not do anything!
First, set up a virtual MIDI port.
• If you are on Microsoft Windows, download and install the loopMIDI software:
https://www.tobias-erichsen.de/software/loopmidi.html
Then create a port. (you only need one)
• macOS already has a virtual MIDI loopback device called the IAC Driver, and you just need to enable it. To do that, open the Audio MIDI Setup application in Utilities. Go to Window -> Show Midi Studio, or press command + 2. Double-click the IAC Driver, and check "Device is online".
• Ubuntu may already have a virtual MIDI port enabled. For more info you'll need to research.
Verify that your ports are working by opening MPP in a WebMIDI-supporting browser (Chrome). You should see your MIDI ports in the MIDI In/Out menu.
Now it's time to play! In your MIDI player program, connect the MIDI out to the virtual MIDI device. MPP will automatically connect to the MIDI device as input, and that's it! Now just play a file, and it should play in MPP. Remember to press Backspace to turn off sustain (release sustain pedal) so that the MIDI can release notes.