With a rhythm-game type app, you can dictate what the user is supposed to be playing. With a sheet music app, not so much. People will want to play the first

With a rhythm-game type app, you can dictate what the user is supposed to be playing. With a sheet music app, not so much. People will want to play the first few measures over and over, try something again after messing it up, stop and take it from the top and so on. If you turn the page too soon or scroll the music the user is playing off the screen, the customer reviews are going to look like Armageddon has come. The only way I see that works understandably and well enough is to recognize when the last measure of the last staff is completed. Even that may be incompatible with some music, but it should work well enough in general.