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For a project I need to handle audio in an iPhone app quite special and hope somebody may point me in the right direction.

Lets say you have a fixed set of up to thirty audio files of the same length (2-3 sec, non-compressed). While a que is playing from one audio file it should be able to update parameters that makes the playing continue from another audio file from the same timestamp the previous audiofile ended playing. If the different audio files is different versions of heavely filtered audio it should be possible to "slide" between them an get the impression that you applied the filter directly. The filtering is at the moment not possible to achive in realtime on an iPhone, therefore the prerendered files.

If A B and C is different audio files I like to be able to:

Play A without interruption:

Start AAAAAAAAAAAAA Stop

Or start play A and continue over in B and then C, initiated while playing

Start AAABBBBBBBBCC Stop

Ideally is should be possible to play two er more ques at the same time. Latency is not that important, but the skipping between files should ideally not produce clicks or delays.

I have looked into using Audio Queue Services (which look like hell to dive into) and sniffed on OpenAl. Could anyone give me a ruff overview and a general direction I can spend the next days burried into?

Spispeas
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2 Answers2

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Try using the iOS Audio Unit API, particularly a mixer unit connected to RemoteIO for audio output.

hotpaw2
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  • Thanks for the input! Audio Units should definitally work, but it still is as low as you can go and hard to master. I have two months experience in iOS programming and hoped for some higher level libraries that could pull this off. Any ideas in that direction? OpenAl? Tried FMOD but could not get the skipping to work. – Spispeas Mar 06 '12 at 09:29
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I managed to do this by using FMOD Designer. FMOD (http://www.fmod.org/) is a sound design framework for game development, that supports iOS development. I made a multitrack-event in FMOD Designer with different layers for each sound clip. Add a parameter in the horizontal bar that lets you controll which sound clip to play in realtime. The trick is to let each soundclip continue over the whole bar and controll which sound that is beeing heard by using a volume effect (0-100%) like in the attached picture. In that way you are ensured that skipping between files follow the same timecode. I have tried this successfully with up to thirty layers, but experienced some double playing. This seemed to dissapear if I cut the number down to fifteen.

It should be possible to use iOS Audio Unit API if you are comfortable with this, but for those of us that like the most simple sollution FMOD is quite good :) Thanks to Ellen S for the sollution tip!

Screenshot of the multitrack-event in FMOD Designer: https://plus.google.com/photos/106278910734599034045/albums/5723469198734595793?authkey=CNSIkbyYw8PM2wE

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Spispeas
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