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AudioFile data format falsely indicating VBR on CBR files
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AudioFile data format falsely indicating VBR on CBR files


  • Subject: AudioFile data format falsely indicating VBR on CBR files
  • From: Jens Alfke <email@hidden>
  • Date: Thu, 14 Feb 2008 10:38:02 -0800

When I open an AudioFile on a constant-bit-rate MP3 file, and access the kAudioFilePropertyDataFormat property, the struct returned always shows mBytesPerPacket==0. Apparently that value indicates that the file is VBR. But I get this on every MP3 file I've tried, even ones I know for certain are CBR.

The code I'm using is based on the aqplay.cpp sample, where after getting the data format it does:
bool isFormatVBR = (_info->mDataFormat.mBytesPerPacket == 0 || _info->mDataFormat.mFramesPerPacket == 0);


So is aqplay.cpp incorrect in how it tests for VBR, or is AudioFile returning incorrect data?

—Jens _______________________________________________
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