Here is what I want to do. If I plug in my Galaxy S4 to my BMW 335i, then I can browse and play music stored on the device just fine and the sound quality is excellent. If I play over the audio auxillary input, I can play anything but the quality of the sound is not good at all. The only way to play system sound and services like Spotify, Pandora, Google Music, etc is though the aux input jack since MTP doesn't carry the Android devices audio output.
What I want to do is transmit all system audio over MTP when the device is connected. This should be doable through some app or through some custom code that would basically buffer the system audio output and push it over mtp. Ideally, you could just browse to an item in the BMW iDrive that says "System Audio" and then you could hear any output from the Android phone regardless of what app is playing it.
Does anyone know of an app that would route system audio over the MTP connection? or does anyone have a service or custom code that would route all audio over the connection?
I have the same problem with Bluetooth audio as well. The 2010 BMW I have doesn't support Bluetooth Audio, but I really don't care about that since that sound quality is pretty questionable as well anyway.