BT audio to mass storage adapter? where to begin?

[slow_rider]

I have a device which has a USB connector that expects to see a mass storage device with MP3 files and possibly others it won't recognize. I would like to build an adapter that can connect to my phone via Bluetooth so that it would seem to the device I have actually connected my phone as a mass storage device, an option that used to be available in Android phones but Google killed it.

Any thought about how to implement this or how to approach the problem?
I have a lot of background in MCUs and such but never had to do something like this.

[Rasz]

no need to build anything, wireless sd card and usb sd card reader

[slow_rider]

That's close, but not there... my phone does not have a full size SD card connector and the microSD is hidden inside and can't be easily accessed.

[Rasz]

you dont need anything in the phone, you connect to the sd card over wifi,. its wireless

[viperidae]

Google had good reason to drop mass storage in favour of mtp.
It might be possible to convert from mtp to mass storage

[Rasz]

It might be possible to convert from mtp to mass storage

why would you bother when you can wirelessly upload files to the SD card in SD reader