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ExtAudioFile and (AAC) bit rates
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ExtAudioFile and (AAC) bit rates


  • Subject: ExtAudioFile and (AAC) bit rates
  • From: Ian Esten <email@hidden>
  • Date: Wed, 03 Aug 2011 13:09:19 -0700

Hi all,

A strange issue has been discovered with our audio file reading/writing classes. What we are doing is using ExtAudioFileRead to read a wav file and ExtAudioFileWrite to write an AAC file. We allow users to select a bitrate up to 320kbps. We always write 44.1kHz files, but allow reading of audio files at any sample rate and allowing ExtAudioFileRead to do the sample rate conversion.

This all works fine, until you try to read do this with 48kHz audio files.

What we do is first create a reader that reads a 48kHz wav file at 44.1kHz (so it creates an AudioConverter to do so). We then write to a 44.1kHz AAC file (so a second AudioConverter is created for that). This works fine too, except that when you do this, the AudioConverter associated with the writer no longer has the 320kbps bit rate available.

I've checked everything is being done as recommended. I've also checked everything that is related to sample rate and bit rates and there are no discrepancies there.

This seems like a problem inside CoreAudio. Any insight would be appreciated.

Thanks,
Ian

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