Use your app package name to define the correct path :
mp.setDataSource("android.resource://<YOURPACKAGE_NAME>/raw/backgroundbeat");
example:
mp.setDataSource("android.resource://com.jorgesys.myapp/raw/backgroundbeat");
or other way to load a media file from /raw
folder, if you are inside an activity you could use:
mp = MediaPlayer.create(this, R.raw.backgroundbeat);
or You can use a VideoView to play your file Videoview on splash screen