Combining AVAudioPCMBuffers. Assumes non interleaved format

AVAudioPCMBuffer+Additions.m

@implementation AVAudioPCMBuffer (LiveAdditions)
  
- (AVAudioPCMBuffer *)combineWithBuffer:(AVAudioPCMBuffer *)buffer {
    if (![buffer.format isEqual:self.format]) {
        return nil;
    }
    
    AVAudioPCMBuffer *combined = [[AVAudioPCMBuffer alloc] initWithPCMFormat:self.format frameCapacity:self.frameCapacity + buffer.frameCapacity];
    
    combined.frameLength = self.frameLength + buffer.frameLength;
    
    if (self.int16ChannelData && combined.int16ChannelData) {
        for (AVAudioChannelCount i = 0; i < self.format.channelCount; i++) {
            memcpy(combined.int16ChannelData[i], self.int16ChannelData[i], self.frameLength * self.format.streamDescription->mBytesPerFrame);
            memcpy(combined.int16ChannelData[i] + self.frameLength, buffer.int16ChannelData[i], buffer.frameLength * self.format.streamDescription->mBytesPerFrame);
        }
    }
    else if (self.floatChannelData && combined.floatChannelData) {
        for (AVAudioChannelCount i = 0; i < self.format.channelCount; i++) {
            memcpy(combined.floatChannelData[i], self.floatChannelData[i], self.frameLength * self.format.streamDescription->mBytesPerFrame);
            
            memcpy(combined.floatChannelData[i] + self.frameLength, buffer.floatChannelData[i], buffer.frameLength * self.format.streamDescription->mBytesPerFrame);
        }
    }
    else if (self.int32ChannelData && combined.int32ChannelData) {
        for (AVAudioChannelCount i = 0; i < self.format.channelCount; i++) {
            memcpy(combined.int32ChannelData[i], self.int32ChannelData[i], self.frameLength * self.format.streamDescription->mBytesPerFrame);
            memcpy(combined.int32ChannelData[i] + self.frameLength, buffer.int32ChannelData[i], buffer.frameLength * self.format.streamDescription->mBytesPerFrame);
        }
    }
    else {
        NSParameterAssert(NO);
    }
    
    return combined;
}

@end