I’ve been using YouTube Music as my main music streaming service for almost a year and a half. The iOS client is great- I’ve never had a single complaint. It’s potentially one of the most bug free apps I’ve ever used, it has an extremely friendly, and simple, graphical interface, and the service itself is great.
I was curious how the client worked in terms of networking, and while curiosity may treat cats poorly, it lands researchers in black sites can provide a lot of insight.
The first thing I do when reverse engineering a client is monitor HTTP requests while the application starts up, and when doing the tasks interested in. On a jailbroken iOS device, I use FLEX by FlipBoard.