Re: iTunes music files
Re: iTunes music files
- Subject: Re: iTunes music files
- From: Chris Adamson <email@hidden>
- Date: Sat, 26 Feb 2011 18:21:42 -0500
Thanks for the link, Kyle. I was just about to reply, but chili got in the way.
Actually, this stuff did get a lot easier in iOS 4.1, thanks to AVAssetReader and AVAssetWriter:
http://www.subfurther.com/blog/2010/12/13/from-ipod-library-to-pcm-samples-in-far-fewer-steps-than-were-previously-necessary/
Still, there's a lot to do for Bruce's problem. He needs to use Media Player to get at the iPod Library and use the special URL from the MPMediaItem to get those files into AV Foundation as AVAssets. The new AVAssetReader / AVAssetWriter stuff makes it a lot easier to get to raw samples from the asset. But that still leaves the rate-change-without-pitch-shift effect. There's a Core Audio unit for this on the Mac, but iOS really doesn't have any effect units of any consequence, nor a plugin system, so it probably requires doing that effect by hand with the converted .caf or .aiff file, and at that point, it may not really matter which playback engine he then uses (Core Audio, OpenAL, AV Foundation and Media Player would all be able to play back the altered PCM from a file). With an effect unit, there'd be a fighting chance of performing the rate shift on the fly - I think you'd risk a delay in the AV Foundation conversion from MP3/AAC to PCM but it would at least be worth trying.
-Chris
Sent from my iPad
On Feb 26, 2011, at 6:05 PM, Kyle Sluder <email@hidden> wrote:
> On Sat, Feb 26, 2011 at 1:06 PM, <email@hidden> wrote:
>> Ideally, we'd like to audio process on the iPad itself to slow down the song without changing the pitch.
>> Or, pre-process off-line to create a file with altered tempo.
>
> Just to clarify, you've got an iPad app and want to access the user's
> on-device iPod library, correct?
>
> http://www.subfurther.com/blog/2010/07/19/from-iphone-media-library-to-pcm-samples-in-dozens-of-confounding-potentially-lossy-steps/
>
> --Kyle Sluder
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