you could do that and make it look like shit, or you could...
1. playdemo <demo name>
2. startmovie <demo name> <FPS you want to record it in>
3. Wait
4. There should be a bunch of pictures in your cstrike folder, use a program called VideoMach to compile them.
but if you want to just use youtube, don't bother in doing this.. cause it looks like **** either way.
~ Thizz King
for youtube better quality: type &fmt=18 at the end of the URL, and refresh.