Re: Getting PCM data from MP3/AAC/ALAC File

Subject: Re: Getting PCM data from MP3/AAC/ALAC File

From: Daniel Staudigel <email@hidden>

Date: Wed, 17 Dec 2008 15:22:01 -0800

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Sorry to spam the list with already-answered questions. Further poking around the list revealed that the answer lies on my own hard drive. Kevin Avila's response to essentially the same question (May 1 2006) is quoted here for interest's sake.

The modern (and easy) way I would recommend to accomplish this task would be to use QuickTime 7's AudioExtraction APIs. Check out the ADC sample codes:

SimpleAudioExtraction - http://developer.apple.com/samplecode/SimpleAudioExtraction/SimpleAudioExtraction.html
QTAudioExtractionPanel - http://developer.apple.com/samplecode/QTAudioExtractionPanel/QTAudioExtractionPanel.html
ExtractMovieAudioToAIFF - http://developer.apple.com/samplecode/ExtractMovieAudioToAIFF/ExtractMovieAudioToAIFF.html

There is also some very good documentation on these APIs

http://developer.apple.com/quicktime/audioextraction.html
http://developer.apple.com/qa/qa2006/qa1469.html

The other method I would recommend is using CoreAudio's AudioConverter APIs.

sample: /Developer/Examples/CoreAudio/Services/AudioFileTools/
/Developer/Examples/CoreAudio/PublicUtility/CAAudioConverter

documentation: /Developer/Examples/CoreAudio/Documentation/AudioToolbox/AudioConverter/

Kevin Avila
DTS Audio Engineer
World Wide Developer Relations
Apple Computer, Inc.

Thanks Kevin! Sorry list!

Daniel Staudigel

On Dec 17, 2008, at 3:14 PM, Daniel Staudigel wrote:

I am trying to get a PCM stream out of out of a generic audio file. So far, I have tried:

1) Opening it with AudioFile, then trying to pipe it through a the appropriate AudioConverter, using AudioBufferFillComplexBuffer. This fails either silently (when trying to play the PCM data), or crashes because of a buffer overrun during the conversion step

2) Opening it with ExtAudioFile with the Client format set to be the desired PCM data. This fails either by playing completely garbled noise (not white noise, which is what I'd expect if it were playing MP3/AAC data as if it were PCM), or by playing nothing, or crashing in a similar buffer-overrun situation as above.

Poking around the lists I saw a reference to an old piece of sample code (ConvertFile?) that I can't get ahold of anymore. Does anybody have this, or something similar?

This seems like it should be easy. I am not familiar with CoreAudio or AudioToolbox, but I've spent enough hours on this that I am reaching out for help!

Cheers,

Daniel Staudigel

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>Getting PCM data from MP3/AAC/ALAC File (From: Daniel Staudigel <email@hidden>)