Hardware Codec Policy Keys
Indicates how an audio queue should choose between hardware and software implementations of a codec.
Overview
If the designated codec implementation is not available, or if a hardware codec is chosen and the audio session category does not permit use of hardware codecs, your attempts to call the AudioQueuePrime(_:_:_:) or AudioQueueStart(_:_:) functions will fail.
Use the kAudioFormatProperty_Encoders or kAudioFormatProperty_Decoders properties to determine whether the codec you are interested in using is available in hardware form, software, or both. See the discussion for kAudioFormatProperty_HardwareCodecCapabilities.
The system does not permit you to change the value associated with the kAudioQueueProperty_HardwareCodecPolicy key while the audio queue is primed or running. Changing the value at other times may cause codec settings to be lost.