Undocument recently informed me of an astounding tool from EndlessVideo.com. What does it do? It allows you to repeat and loop any YouTube Video at any point in time. Here's the easiest way to immediately implement its power:
Observe the URL up above in your browser.
Example: http://www.youtube.com/watch?v=8q3ag_of9y0
Now, simply add "endless" in front of "youtube"
Example: http://www.endlessyoutube.com/watch?v=8q3ag_of9y0
Press enter and presto! you have a youtube video looping! You can even share the link with the included loop points that you made. You can try DJ'ing with it but it may take a while to get a correct loop (it's not very precise) or you can play along on your instrument of choice while the song plays over and over.
Shared loop points example:
