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POExtract iPod Library raw PCM samples and play with sound effects
 

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    <p>I am trying to extract raw PCM samples from an MP3 in the iPod Library so that I can play the song and manipulate the pitch, tempo, and apply sound effects (such as filters). I have already gone down the route of AVPlayer and AVAudioPlayer which both do not allow very much control over the playback at all.</p> <p>The code below is as far as I have gotten with this. I am at a point now where I do not know what to do with the CMSampleBufferRef's in my while loop because I do not know which framework to use in order to playback the audio and apply such effects.</p> <p>Any idea what would be the best approach to achieve this? I have looked at cases where the file is converted using an AVAssetWriter but this is not going to cut it for me because the process is too time consuming. Surely I can just read the PCM samples into memory for playback without having to write them to disk first?</p> <p>NB: I know the code below references an mp3 within the project but I am aware that this approach will work the same as if I were pulling an NSURL from the MPMediaPropertyAssetURL</p> <pre> <code> -(IBAction)loadTrack:(id)sender { NSString *songPath = [[NSBundle mainBundle] pathForResource:@"Smooth_Sub Focus_192" ofType:@"mp3"]; NSURL *assetURL = [[NSURL alloc] initFileURLWithPath:songPath]; AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil]; NSError *assetError = nil; AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:songAsset error:&assetError] retain]; if (assetError) { NSLog (@"Error: %@", assetError); return; } AVAssetReaderOutput *assetReaderOutput = [[AVAssetReaderAudioMixOutput assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks audioSettings: nil] retain]; if (![assetReader canAddOutput:assetReaderOutput]) { NSLog (@"Incompatible Asser Reader Output"); return; } [assetReader addOutput: assetReaderOutput]; [assetReader startReading]; CMSampleBufferRef nextBuffer; while (nextBuffer = [assetReaderOutput copyNextSampleBuffer]) { /* What Do I Do Here? */ } [assetReader release]; [assetReaderOutput release]; } </code> </pre>
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