CODEWITHSUNDEEP
iphoneiosaudiocore-audioaudioqueue
Sergey Kopanev
Sergey Kopanev

Reputation: 1504

How to get samples from AudioQueue Services on iOS

I'm trying to get samples from AudioQueue to show spectrum of music (like in iTunes) on iPhone.

Ive read a lot of posts but almost all asks about get samples when Recording, not playing :(

I'm using AudioQueue Services for streaming audio. Please help to understanding next points: 1/ Where can I get access to samples (PCM, non mp3 (I'm using mp3 stream) 2/ Should I collect samples in my own buffer to apply fft ? 3/ Is it possible get frequencies without fft transformations ? 4/ How can I synchronize my fft shift in buffer with current playing samples ?

thanks,

update:

AudioQueueProcessingTapNew

For iOS6+, this works fine for me. But what about iOS5 ?

Upvotes: 0

Views: 715

Answers (1)

hotpaw2
hotpaw2

Reputation: 70743

For playing audio, the idea is to get at the samples before you feed them to the Audio Queue callback. You may need to convert any compressed audio file format into raw PCM samples beforehand. This can be done using one of the AVFoundation converter or file reader services.

You can then copy frames of data from the same source used to feed the Audio Queue callback buffers, and apply your FFT or other DSP for visualization to them.

You can use either FFTs or a bank of band-pass filters to get frequency info, but the FFT is very efficient at this.

Synchronization needs to done by trial-and-error, as Apple does not specify exact audio and view graphic display latencies, which may differ between iOS devices and OS versions anyway. But short Audio Queue buffers or using the RemoteIO Audio Unit may give you better control of the audio latency, and OpenGL ES will give you better control of the graphic latency.

Upvotes: 1

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