I have written two applications which are now on Goggle Play.
It changes the user interface to play music files by people whose understanding is limited to simple one push actions.
Dementia Player 2 is for Android 4.4 and above as the file system changed in 4.4, you know have to use a file extension to access music files using player in Thunkable.
Dementia Player 2
Dementia Player 1 is for Android 4.0 to 4.3 which uses the documented source code for accessing music files.
DementiaPlayer1