Question

Weeks ago, I posted this thread regarding problems I was having with AVAssetWriter: AVAssetWriter Woes

Further research seems to lead to a conflict using AVAssetWriter while playing audio with AVAudioPlayer or, really, any audio system. I tried with OpenAL as well.

Here’s the background:

• Using AVAssetWriter to write frames to a video from an image or set of images works fine UNTIL [AVAudioPlayer play] is called.

• This only happens on the device, not the sim.

• The error occurs when attempting to create a pixel buffer from CVPixelBufferPoolCreatePixelBuffer.

• Once the audio starts playing, the AVAssetWriterInputPixelBufferAdaptor.pixelBufferPool which existed before suddely becomes nil.

You can download the representative project here: http://www.mediafire.com/?5k7kqyvtbfdgdgv

Comment out AVAudioPlayer play and it will work on the device.

Any clues are appreciated.

Answer 1

I’ve found the solution to this issue.

If you want to have AVAudioPlayer and AVAssetWriter behave correctly together, you must have and audio session category that is ‘mixable’.

You can use a category that is mixable like AVAudioSessionCategoryAmbient.

However, I needed to use AVAudioSessionCategoryPlayAndRecord.

You can set any category to be mixable by implementing this:

OSStatus propertySetError = 0;

UInt32 allowMixing = true;

propertySetError = AudioSessionSetProperty (
                       kAudioSessionProperty_OverrideCategoryMixWithOthers,  // 1
                       sizeof (allowMixing),                                 // 2
                       &allowMixing                                          // 3
                   );