Playing MIDI on tvOS

According to Apple’s App Programming Guide for tvOS, AVFoundation is supported in tvOS.

Groovy!

Let’s use AVMIDIPlayer to play a file!

Set up

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AVMIDIPlayer’s init func wants two URLs: one to a MIDI file and another to a SoundFont or DLS file.

I created a standard MIDI file in Sibelius. The SoundFont I used is the one distributed with MusesCore.

Here is how I created the player.

And then I played it by calling the cunningly named play() function. I use a completion handler to reset the playback position.

This is pretty much what I do in iOS and Cocoa and it works.

The result

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In the tvOS simulator, it works almost OK. You hear sine waves – just like in iOS. When you run it on an actual device, you should hear the instruments.

In tvOS, not so much. I hear two notes with a loaded instrument, and then blammo.
Crash.

Removing the dispatch_async call yields the same result.

Here is the love letter from the debugger.

By the way, I also tried MusicPlayer and Core Audio since the guide says AudioToolbox and AudioUnit are supported too. Same result. The stack trace shows that error occurs deep in the bowels of AudioToolbox.

Summary

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Well, crap. It would be nice to be able to play MIDI files; I’d like to port my ear training app to tvOS. But without playback, it would be reaaalllly hard to recognize and identify the intervals, chords, and scales playing.

Update

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I spent far too much time on this. I looked at my code over and over again. I was certain that I was doing it correctly (but there is always that doubt every developer deals with), so why was it crashing?

It wasn’t my code.

It was the MusesScore sound font. Out of desperation, I tried another sound font and the sun started shining , the birds sang, and my cat’s litter box was magically clean. Oh, and it played on the AppleTV.

Resources

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