gistfile1.m

    // extract RAW PCM
    NSURL* url = [[NSBundle mainBundle] URLForResource:@"" withExtension:@"mp3"];
    AVAsset* asset = [AVAsset assetWithURL:url];
    NSError* err = nil;
    AVAssetReader* reader = [[AVAssetReader alloc] initWithAsset:asset error:&err];
    if (!err) {
        AVAssetReaderAudioMixOutput* output = [[AVAssetReaderAudioMixOutput alloc]
                                               initWithAudioTracks:[asset tracksWithMediaType:AVMediaTypeAudio]
                                               audioSettings:nil];
        [reader addOutput:output];
        [reader startReading];
        
        CMSampleBufferRef sampleBuffer = NULL;
        while (1) {
            sampleBuffer = [output copyNextSampleBuffer];
            if (sampleBuffer == NULL) break;    // there are no more sample buffers available
            
            CMBlockBufferRef blockBuffer = NULL;
            AudioBufferList audioBufferList;
            
            OSStatus status = CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer,
                                                                                      NULL,
                                                                                      &audioBufferList,
                                                                                      sizeof(audioBufferList),
                                                                                      NULL,
                                                                                      NULL,
                                                                                      0,
                                                                                      &blockBuffer);
            if (status == noErr) {
                // ここでAudioBufferListから読み出す処理など
            }
            
            if (sampleBuffer) CFRelease(sampleBuffer);
            if (blockBuffer) CFRelease(blockBuffer);
            if (status != noErr) break;
        }
    }