AVAssetWriter / AVAudioPlayer Conflict?

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
                   );

Answer 2

This above answer is in complete. It doesn't work. Do this instead

// Setup to be able to record global sounds (preexisting app sounds)
    NSError *sessionError = nil;
    if ([[AVAudioSession sharedInstance] respondsToSelector:@selector(setCategory:withOptions:error:)])
        [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:AVAudioSessionCategoryOptionDuckOthers error:&sessionError];
    else
        [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:&sessionError];

    // Set the audio session to be active
    [[AVAudioSession sharedInstance] setActive:YES error:&sessionError];

//then call your asset writer 
movieWriter = [[AVAssetWriter alloc] initWithMovieURL:movieURL size:CGSizeMake(480.0, 640.0)];