Taken from http://lifehacker.com/the-six-best-youtube-url-tricks-1422544868
Some of these tips involve NON-youtube sites, and may change over time.
- REPEAT: If you need to playback a video automatically, you can add the word “repeater” after “youtube” in the URL to open it in an external site that will play it back as often as you let it. You can also set it to play back just part of the video. So youtube.com/watch?v=kfVsfOSbJY0 becomes youtuberepeater.com/watch?v=kfVsfOSbJY0
- DOWNLOAD: Just add “pwn” to the URL before “youtube” and you’ll be taken to an external site with multiple options for download formats. For example: youtube.com/watch?v=Sagg08DrO5U becomes pwnyoutube.com/watch?v=Sagg08DrO5U
- NOT AVAILABLE IN YOUR COUNTRY: If you’re looking to get to a video that has some form of restriction on it, change the format of the video link from watch?v=IEIWdEDFlQY to /v/IEIWdEDFlQY
- START IN THE MIDDLE: If you need to point someone to a certain portion of a video, you can always right click on the player and select “Copy video URL at current time.” However, if you need to be especially specific, you can modify the end variable that follows “t=X” where X is the number of seconds into the video that you want the player to start at. So the good part isn’t here: youtube.com/watch?v=9R6Ibz31DtE It’s here: youtube.com/watch?v=9R6Ibz31DtE#t=114
- DISABLE RELATED VIDEOS: It doesn’t happen often, but sometimes the related videos that are shown at the end of a video can be unsavory. Or, perhaps you just find them irritating. If you want to disable the array of options that show up when the clip’s done playing, add “&rel=0” to the end of the URL in the embed code. Change src=”//www.youtube.com/embed/T0-2lzA7_Cg” to src=”//www.youtube.com/embed/T0-2lzA7_Cg?rel=0″
- SKIP THE BORING PARTS: Just how much of your time on YouTube is wasted watching the boring parts of a video while waiting for the main event to begin? If you believe Wadsworth, the answer is about 30%. While it started as a joke, Google took it seriously enough to add the feature to YouTube itself. If you want to skip the unimportant intros, just add “&wadsworth=1” to the end of the URL. So this URL: youtube.com/watch?v=c0KYU2j0TM4 becomes youtube.com/watch?v=c0KYU2j0TM4&wadsworth=1