how to pass asset file path in the method getAssets().openFd(string)

I have a file in the android resource res/assets/audio.mp3

How to pass the file to the method getAssets().openFd(string)

I need the exact file path. I tried using R.raw.xxx But my requirement is to pass the file path as string.

If this is not possible kindly tell me another way of accessing it but only using a valid string path

Kindly help.