I think all video hosting sites, like YouTube and Vimeo use software that compares the video audio to some database (or many databases) of music. If the video audio is close to a audio file in the database it flags it as copyright material. That's my opinion. I've never really researched that but it makes sense.
I wonder if you could use audacity to insert a high pitch tone (too high for human hearing) every 10-15 seconds in the audio file to throw that off? If that's how they do it, then it should work. But I can't try this anytime soon, maybe someone could give it a try and see what happens.
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