Was just curious this weekend (I'm an iOS engineer by day) how to find out which codec your iOS device uses to communicate to bluetooth headphones. There are numerous tutorials on this matter for macOS (OSX) on the Internet, Alt+Click, Bluetooth Explorer and friends, but nothing on iOS. That's why I decided to compose this tutorial for you, requires looking into console log and some keyboard munching. (wanted to insert screenshots here but have no rights as I'm very fresh to head-fi. Version with screenshots here: https://stackoverflow.com/questions/22639691/how-to-determine-which-codecs-a-bluetooth-device-supports-over-a2dp/42190656) Here we go: 1. Connect your iOS device to your Mac, answer Trust on the iOS device if you haven't done this before. 2. Open Console.app. 3. Select your iOS device on the left sidebar. 4. Type `bluetooth` in the top-right search bar, press Enter and select `Subsystem` instead of `All`. 5. Now, start playing to your bluetooth headphones on the iOS device (codec activates only when you output sound). 6. Press `Cmd+F` and search for `Starting a2dp send thread` in your console messages. 7. You'll see used codec in `codec: ` field. Values are the same as specified in Bluetooth specs. Basically `0 = SBC`, `2 = AAC`. Was very surprised, though, that a pair of headphones I just bought from very adored and award-winning manufacturer (not Sennheiser) does not have AAC codec in them, despite having that in specifications (will not name them here, contacting their tech support for clarification). Feel free to publish your experience and discoveries here.