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What does AVEncoderAudioQualityKey do?

According to meager documents AVEncoderAudioQualityKeys -

The keys that determine the quality of the sample rate conversion are used for the AVSampleRateConverterAudioQualityKey property.

 enum { AVAudioQualityMin = 0, AVAudioQualityLow = 0x20, AVAudioQualityMedium = 0x40, AVAudioQualityHigh = 0x60, AVAudioQualityMax = 0x7F }; typedef NSInteger AVAudioQuality;

Testing with AVAudioRecorder is practically no different from the size or quality of an audio file during a 2-minute recording recorded with AVAudioQualityMin compared to recording with AVAudioQualityMax . The test used a sampling frequency of 8 kHz using kAudioFormatMPEG4AAC .

Can someone enlighten me on the theoretical and practical purpose of this key?

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These keys are used to indicate quality in conversions with a sampling rate. An audio file format that determines the sample rate and bit depth determines the size of your file. According to Apple docs , they are:

The keys that determine the quality of the sample rate conversion used for the AVSampleRateConverterAudioQualityKey property.

So, these quality keys only determine how well you want to reprogram the audio into a different format.

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Source: https://habr.com/ru/post/896332/

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