I seriously doubt it. It would have to be built into the YouTube interface. Something like that has to reside on a server/computer, not in some virtual space between the user and web page. Best you can do is get a file (download) and do it on your computer.
You may already know this, but the latest version of RealPlayer, which you can download for free off the Internet, will allow you to download any YouTube Video. In fact, mine asks me every time if I want to download whatever YouTube I'm watching. Then there is a program called SloMo Director that can slow video down and loop whatever sections of it you want to see, but keep the pitch the same. HOWEVER, there is a step you need to do inbetween, and you need another program for that. Since all YouTubes are flv files, and SloMo only works on avi files, you need a converter software. I use AVS4You. So the sequence goes like this: Find a YouTube you like, download the file with RealPlayer, convert it with AVS4You, play it with SloMo Director. The two programs together will cost you about $100. Make sure and download ALL the SloMo stuff. If you want to do this and need help, e-mail me and I'll give you my phone #.
What I do (did), simple enough:
1. download YouTube downloader,
2. download a file, (comes in as .flv file) and convert it to a .wmv file with YouTube downloader,
3. play it with a new version of Windows media player.
4. Adjust the tempo down to half speed.
The only problem is that the synchonization goes wrong most of the time: the image will come slightly before the sound; you see the flappers moving before you hear the actual notes.
Quite simple actually, but not at all perfect. But it helps!
I was just reading last night that Mozilla's
Firefox (a free alternative to Microsoft's
Internet Explorer) can be beefed up with a plug-in
called "grease-monkey" (also free) that allows
one to download from youtube and save files.
Yeah, its going to have to be something in your desktop. Web apps don't normally run like that. And the only way to do that is to get a file from the web to your desktop.
.. which is really not hard to do. It's just the problem of getting video and sound in sync. I'm sure somebody somewhere in this ol'world must be working on it ..
There is a program that just finished beta testing a week ago, that does exactly what you're asking. The website is www.enounce.com, and the program is called "My Speed." I have one of their previous versions, which slowed down video on either real player, or windows media player. The My Speed program, for any kind of flash video, goes up to about a hundred bucks. The more economical way to do it is to use Real Player's latest version to download the videos as others have mentioned. Then, purchase the Enounce version that slows down videos on Real Player, which I think is about $40, and you're good to go - couldn't be easier. I've been using it for a couple of years, and it works great - slows the video all the way down to .3