How to sync code callbacks to playback time of an audio track?

Question

I have a presentation audio track playing in an iPhone app for which I want to show specific interactive "slides" at specific playback times. The reason why I cannot use video is that the slides are interactive (not just photos).

A developer recently said that you can't trust start playing an audio track and then display content triggered by a timer. The longer the track the more the timer will fire aside because media playback varies in real played length.

Are there callbacks which I can receive such as "arrived at playing time X:Y" or a callback that fires every played second?

@estobbart is on the money with this. You have to synchronize with callbacks from AudioUnit. Maintaining an NSTimer on a separate thread would never work reliably. — Max MacLeod, Nov 15 '12 at 14:12

score 2 · Accepted Answer · answered Nov 15 '12 at 14:05

2

An AudioUnit has a callback property you can set which you pass in an AURenderCallbackStruct. That callback will have a timestamp.

OSStatus YourAURenderCallack (
   void                        *inRefCon,
   AudioUnitRenderActionFlags  *ioActionFlags,
   const AudioTimeStamp        *inTimeStamp,
   UInt32                      inBusNumber,
   UInt32                      inNumberFrames,
   AudioBufferList             *ioData
);

answered Nov 15 '12 at 14:05

estobbart

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Thank you @estobbart - do you know of a working example that plays a file using a callback like this? – Proud Member Nov 15 '12 at 14:36
This is a pretty detailed write up. http://atastypixel.com/blog/using-remoteio-audio-unit/ – estobbart Nov 15 '12 at 14:43

How to sync code callbacks to playback time of an audio track?

1 Answers1