Is using a song for a skate/unicycle video illegal?
Technically not if you are using it for your own sake. If you aren’t using it to make money it should be fine. That is why youtube wont let you monetize your video if you don’t have all the rights.
Has YouTube started letting you use music again without a complicated rights process? I had videos that were blocked a few years ago after YouTube said I was using “3rd party content.” They even flagged a couple videos where I used stock iMovie music, which I thought was bizarre.
It depends much on the song. But if you’re using the music that you don’t have rights to, sometimes your video works perfectly, but then in other countries it is impossible to view due to copyrights issues.
I guess if it is legal or not depends also on the country you’re in.
Most of the time yes, unless the music was released as ‘royalty free’ or creative commons. Generally this will be clearly stated and most of the time you can’t make any money from any videos you make with it (legally that is).
Moby releases a lot of his music for free, for example, on mobygratis.
Unicycle videos
Hey guys, I make unycycling videos, please come check out ! I am a new rider so don’t be surprise if you don’t find me so good ! But, I would really appreciate if you could take the time to go see my videos and if you like them or want to support me, please, like, comment, share and subscribe to my channel ! 
