I made a small correction to your app regarding the slider. If the music is paused and the slider position is changed, the player starts immediately. This should not be the case and can be adjusted as follows:
Another thing that is usually expected from a music player is that when you fast forward or rewind, the sound remains audible even during this fast forward/rewind. This is useful, among other things, if you want to find a specific point in a music track. This should not be possible with the on-board Slider component. I used @Ken's SliderTools (four years ago) for this:
