I am currently creating an app that plays music. I would like to add a feature that shows the music lyrics while the music plays, with the current position of the text marke
Most Karaoke apps these days use the .Kar file extension. It's a slightly butchered MIDI file with some annotations and it's pretty small in file size.
I have no idea where you'd start to read it though. You could ask these guys: http://www.ikaraokeapp.com/
Most little devs are happy to help others out.