Hi Luther, I've not done MIDI on iOS yet, but Mac OS X provides CoreMIDI. CoreMIDI handles time stamping for recording and playback, so you don't have to. There are a few different ways to use CoreMIDI, and some leave more of the work up to your app. Generally, if you're handling all data scheduling, then you merely need to pick a reliable time period and make sure that all of your MIDI events are handed to CoreMIDI slightly before their time stamp requires them to fire. This time period allows the CoreMIDI API some time to pass the data along to the interface, potentially taking advantage of technology such as MTS. Even dynamically generated MIDI should work flawlessly without significant latency. Recording is similar, in that all the data you receive will have a time stamp generated by CoreMIDI. The only exception to the above is that some software MIDI endpoints do not have automatic scheduling (but all MIDI hardware does have scheduling handled by CoreMIDI and the OS).
A quick check of the internet hints that CoreMIDI was added to iOS 4.2, which sounds like a long time ago. None of my clients have needed MIDI support, so I don't know any details of whether CoreMIDI differs between OSX and iOS. As Paul Davis has mentioned, CoreAudio provides clocks that allow you to figure out what time stamps to apply to outgoing MIDI, so that CoreMIDI will align the MIDI events to audio. Same for incoming MIDI - the time stamps can be compared to CoreAudio clocks for reference. This is a deep subject, though, because CoreAudio has tons of information about the latency between time stamps in your code and the actual audio events on the other side of your audio interfaces. You'll need to take these latencies into account if you want perfect alignment between audio and MIDI. Thankfully, Apple has done the hard work of making the information available to the application, but you need to figure out how to obtain all of this information from the various sources (buffer delays, interface conversion delays, bus latency, channel latency, etc.) By the way: Welcome! I have found programming CoreMIDI to be very enjoyable, having worked with MIDI since its inception. Good luck with your sequencer. Brian Willoughby Sound Consulting On Jul 9, 2015, at 9:08 AM, Luther Baker <[email protected]> wrote: > I am interested in writing a MIDI sequencer (iOS and eventually Mac) and was > wondering, amongst other things, what the general consensus was regarding > timers for recording and playback. > > Is there a good open source implementation someone would suggest I read > through? > > I'd be curious what folks suggest for storing the midi information as well as > suggested data structures and strategies for playback. Are most packages > just storing time stamp offsets or are they creating a 384PPQN grid ... and > if so, any high level thoughts on how they manage that grid quickly? > > Would it read like a game ... with a game loop leveraging CADisplayLink > timer? Do I need a high precision timer? etc ... > > I'm hoping someone wrote a white paper to introduce potential gotchas and > hoping someone could lead me in that direction. > > Thanks in advance, > -Luther > _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/coreaudio-api/archive%40mail-archive.com This email sent to [email protected]
