That being said, YouTube now has a solution for that. They’ve quietly added a slow motion feature to the Video Editor and Enhancements tools. Okay, it might make me sound ridiculous but it can be fun to play with. Of course, most basic video editing tools, like iMovie and others, have a slow motion feature. But as YouTube grows, video editing via your browser is something they want to do.
On the Enhancements page, click the turtle icon next to “Stabilize” and pick your speed.
In an Editor project, click the effects icon and check the “Slow motion” box.
Forum discussion at YouTube Help.