video streaming like youtube...

Hey, I'm hoping someone here can point me in the right direction...

I'm looking to offer several long videos on my site and I'd like to offer the ability for people to come back to those videos at a later time and resume where they left off... (basically to pick anywhere in the timeline and watch it right away instead of having to wait for the whole video to download first).

For example, on youtube, you can goto any video and select anywhere in the timeline of that video before anything has downloaded and it will start buffering and playing the video from that point in the timeline....

I'm not even sure what this is called or how it can be done... hopefully someone here knows...

I've been using camtasia to do some screen captures and exporting them to flv and mp4 and when I try to access them via my website I have to wait for the whole video to download before I can skip ahead to maybe 3/4 later in the video. Which isn't a huge deal for a small video, but when I've got 1 hour and 20 minutes of video I don't want people to have to wait 20 minutes before they can watch the last few minutes of the video they missed last time.

Any help would be much appreciated, thanks!

P.S. just hosting the videos on youtube isn't an option as I want these videos to only be available to people who sign up on my site.