Quelle: http://wiki.answers.com/Q/How_do_you...in_slow_motion

You can do it while on the original video if you have a plugin for your browser that allows you to do that (for example 'enounce myspeed'--for a fee). Other people probably download the video and run a program to tweak video (much larger selection of software) then re post it.

[edit]
You can get a trial of SnakeLoops for Mac from www.snakeloops.com . It can slow down YouTube files after installing Perian codecs. You just have to use some 3rd party software for downloading videos from youtube.

[edit]
An alternative is a tool called EmbedPlus (http://www.embedplus.com). Basically, it allows you to add slow motion and other DVD-like controls to your video embeds. There are other features you might find useful if you check out the homepage. Anyhow, it's free and requires no downloading.

Read more: http://wiki.answers.com/Q/How_do_you...#ixzz1FWasqyEw