What data is being transferred in Bluetooth audio distribution profile?

I wonder what data specifically are transferred between a device (e.g. a mobile phone) and bluetooth headphones. This is likely using one of the audio distribution profiles. I am aiming at minimizing anything that could anyhow modify the original audio data.

To put it in an example:

1. I have an MP3 file, the mobile device decompresses the data. I suppose this is not done in a bad way that would influence the sound quality.


2. Magic in the phone and in the transfer.


3. What is now at the input of the headphones? Do I get the exact output of the step no. 1? Or can there be any distractions from the phone bus like for regular sound cards that are built-in the computers?

Many thanks for your answers.