When I tried to sync an extremely paired-down list of songs (16, from 6000), it still takes 10 minutes to index. I suspect it's looking through my entire phone and somehow is exceeding its own memory buffer. Other users have reported to lose ID3 tag indexing when their buffer is exceeded. I have further proof because a 2gb stick with hundreds of songs was able to transfer its ID3 tags no problem.
Anyways, the car uses the MTP protocol. I want the car to only see my media folder. Hence, I need an app that can toggle on/off a "firewall" of sorts so that to the outside world, my music folder becomes the root directory of this MTP folder, and it can't access beyond this sandboxed folder. Does something like this exist? Google came up dry.
Failing that, I wouldn't mind having an app that can achieve this through the USB mass storage protocol.