EDM is Electronic Dance Music. He is creating his own/new music. As he says quickly, "If I could play it, I would, but I have to draw it". Using a computer/mixer/synthesizer and possibly any one of a literal ton of equipment, he is making music on his computer. There may be samples of other music (I don't listen to EDM, but I used to listen to house music and have been known to mess around at my friends home studio) but I believe Deadmau5 is mostly or all original. He could be taking some samples and putting so many effects on it, it would be impossible to recognize (think any sample from a song you know ran through a guitar wah and various distortions). I suspect the original artist/royalties thing would work the same way as usual. But like I said, I am pretty sure these EDM guys mostly make their music from "scratch" using synthesized instruments and effects.
