The ability for youtube, BBC, Vimeo to work is a very simple math.
The incoming connection for the user has to be 'bigger' as a pipe than the data rate for the video.
If you have a 10mb connection, you should be able to watch 8mb video (the general data rate of some HD online) with almost no wait.
So yes, you can do this using FCP & compressor. Now, if you're hosting it yourself, you're dealing with other issues, such as the incoming speed to your offsite host; things you may not be able to control.