Creating a MIDI file from an AKKeyboardView

问题

Currently I am using an AKKeyboardView to connect essentially to the AKRhodesPiano object, and I was wondering if there was an easy way to generate a MIDI file from this?

I see the AKKeyboardView has the noteOn and noteOff functions, which does produce the MIDINoteNumber but I can't find anywhere else in the AudioKit library to really take this input and generate a MIDI file, even if only just a simple one.

回答1:

You would need to run an AKSequencer in the background (maybe with a metronome track). Make an additional track that you will record onto. Also set the length to be as long as you will need for the recording.

When you get a noteOn message from the keyboard, you can check the sequencer's currentPosition and record this into a dictionary. When you get the matching pitch's noteOff message, again check the currentPosition. Use the difference between these two times to get the duration and add a note to your recording track on the sequencer:

myRecordingTrack.add(noteNumber: noteNumber,
              velocity: 127,
              position: timeAtNoteOn,
              duration: timeAtNoteOff - timeAtNoteOn,
              channel: 0)

Then you could easily use AKSequencer's genData() to create a MIDI file (possibly either deleting the metronome track, or copying the recorded track to a new AKSequencer instance).

Check out the SequencerDemo for setting up AKSequencer and building sequences and MIDIFileEditAndSync (both in the iOS Example folder in the AudioKit repo) for an example of writing AKSequencer to a MIDI file.

来源：https://stackoverflow.com/questions/50070105/creating-a-midi-file-from-an-akkeyboardview