Freeda you got me thinking so I did a quick search. It's called YouTube Content ID
YouTube's Content ID creates a fingerprint of uploaded reference material, then compares it not only to newly uploaded videos, but to every video ever uploaded to the video sharing powerhouse. And it does it in minutes.http://www.streamingmedia.com/Articles/ReadArticle.aspx?ArticleID=78358http://www.youtube.com/t/contentid
The system is flexible enough to identify videos only partly comprised of copyrighted material, or where the dimensions or colors are altered. Content owners can create rules to block all pirated material, allow it and track its use, or allow it and monetize its views. Heckmann initially didn't see the value of the allow and track option, but said many content owners were thrilled to get free data on where in the world their content was popular.
Content owners need to upload low-resolution reference files for YouTube to check against. Once YouTube has created a reference file, it compares that to its library of millions of videos, and does it in minutes so that permitted videos can quickly go live. Over 1,000 partners worldwide, including CNN, use the system.
A possible hack? Speed up or slow down audio by 6% or more.http://www.csh.rit.edu/~parallax/