This is a very simple app that loops Calm Rain. It has a start/stop button and a volume button, I consider this app feature complete. There are plenty of apps out there that do this, but are overloaded with features and complexity, so I wanted to have something very minimal. The playback is not interrupted by audio focus, so it can be used alongside other media apps, which makes it ideal as a tinnitus masker.
I was struggling with getting the sound to loop perfectly, the solution is to use MediaPlayer-Extended.
I consider adding this app to google play in the future, but for now I want to test it for a few weeks.