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What I'm trying to do is exactly as the title says, decode multiple compressed audio streams/files - it will be extracted from a modified MP4 file - and do EQ on them in realtime simultaneously.

I have read through most of Apple's docs.

I have tried AudioQueues, but I won't be able to do equalization, as once the compressed audio goes in, it doesn't come out ... so I can't manipulate it.

Audio Units don't seem to have any components to handle decompression of AAC and MP3 - if I'm right it's converter only handles converting from one LPCM format to another.

I have been trying to work out a solution on and off for about a month and a half now.

I'm now thinking, use a 3rd party decoder (god help me; I haven't a clue how to use those, the source code is greek; oh and any recommendations? :x), then feed the decoded-to LPCM into AudioQueues doing EQ at the callback.

Maybe I'm missing something here. Suggestions? :(

WanderingInLimbo
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1 Answers1

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I'm still trying to figure out Core Audio for my own needs, but from what I can understand, you want to use Extended Audio File Services which handles reading and compression for you, producing PCM data you can then hand off to a buffer. The MixerHost sample project provides an example of using ExtAudioFileOpenURL to do this.

VictorB
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    Thanks. I think I more or less solved it with Audio Queue's offline rendering. Tried audio converter service but could not get it to run (got the very informative -50 error). Now I got to figure out how to pass Information from the UI into the callback without running into trouble due to them bring in different threads. I really should update this question of mine with an answer. – WanderingInLimbo Aug 26 '11 at 01:40