Another option is to find royalty-free music. There's heaps of it out there, just do a search. All they composers ask is that they are credited for their work. As for going with other video sites, well, the more popular they get the more they will crack down as well. You see, the owners of the original material (record company's mostly) will keep tabs on their copyrighted material. Don't think so? Try posting a well recognized song, by say... Universal Records, and see how long it lasts.
One more, and I recommend this over everything, is you could get a software (Acid, or Fruity Loops, etc..) and create your own music. It's not that difficult and you can put ques where you want them to emphasize the effect you're performing.
And lastly, I want to clear one more thing up. Copyrights. Here is the short version. Whatever you make, whatever!, is technically copyrighted as soon as you stamp it DONE. This is called "The Poor Man's" copyright. But there is a catch. As soon as you duplicate the original you need to copyright that image, video, music, whatever. You can do so by sending in the right information with a check ($35 per original work, I believe) and you can get the real deal, squeaky clean, all yours copyright, fully legal. Or, you can create a publishing company for yourself. Then what ever you create under your publishing company's name will be copyrighted. No $35 a pop. Anything and everything will be yours. If people want to use it they must go through your association (BMI, ASCAP, etc...) and meet your conditions to use your work. There you have it. That's the quick copyrights 101 course. Want to learn more, go to the library
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John