newbie connection issue, simple question

[ZeeWolf]

In this case car headunit acts as a host, and your phone as a simple storage device (like a pendrive - you may have to set connection type to mass storage on the phone, depending on headunit). This setup uses headunit's internal DAC for playback - so sound quality depends heavily on quality of the headunit. No need for any app - you control playback from headunit. Oh, and most important: you DON'T use OTG cable - just regular one.