The OnAudioPassThru notification sends microphone audio data from the headunit to the mobile device as binary PCM data (preceded by a wav file header). Unfortunately, this data does not match the PCM format requested in the preceding PerformAudioPassThru request from the phone.
For example, PerformAudioPassThru can request microphone audio data in a format of 8-bit PCM at 22KHz but OnAudioPassThru will return data in the OS's default format (ex: 16-bit 44KHz).
Recommend updating the file from_mic_to_file_recorder_thread.cc to set the sampling Hz, the bits-per-sample, and number of channels.