My suggestions:
-give the opportunity application start with or without entering the account and create a buttons of sign in and sign out...
-by the time of sign in... make a graphical way showing that it's loading without "exit the program"...
(personally i dont like when it's exit the application cause it takes long to sing in and then it reenter the app...)
-Add error massage when there isnt internet connection.
-Add volume button AND remove the default yellow bar OR just remove the yellow bar...

These are my Friendly suggestions.... Thanks for the hard work!

Favourites' list and playlists work for me now....
just the (+) buttons, for load the next videos keep some videos from the first search... maybe this is the way you want... or you can change this.