Impossible to control AAC parameters with AVAudioFile writer

Question

Created Aug ’20

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Hello all,

I'm trying to write an AAC-compressed audio file in M4A or CAF file format with AVAudioFile.
I'm using the following settings dictionary:

Code Block swiftsettings = [AVFormatIDKey: kAudioFormatMPEG4AAC,
						AVSampleRateKey: 48000.0,
						AVNumberOfChannelsKey: 2,
						AVEncoderBitRateStrategyKey: AVAudioBitRateStrategy_Variable,
						AVEncoderBitRatePerChannelKey: 64,
						AVEncoderAudioQualityForVBRKey: AVAudioQuality.high,
						AVEncoderBitDepthHintKey: 16] as [String : Any]

Output file is OK, but my issues are

changing the bit rate strategy, the bit rate value or the encoder audio quality has no impact whatsoever on the output file,
switching from CAF to M4A file format with the same settings make a big change in the file size but it should not.

My question is simple:
Is there an issue with my settings dictionary or is it a known issue with AVAudioFile?
I spent quite some time exploring how to build this dictionary on the web and the Apple documentation (very limited on this topic I must say), but I can't find what I do wrong...

More details about this issue are available here :
https://gitlab.com/AudioScientist/avaudiofileaacparameters

Thank you for your help :)

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Answer 1

DigitalAudioTom OP

Sep ’20

Anybody ? 😕

0