There is a very powerful feature of QuickTime that works with "fast start" movies or "rtsp streamed" movies. Since QuickTime 3, users have been able to specify their internet connection speed in the QuickTime Settings Control Panel:
Figure 1 , QuickTime Settings Control Panel
On the server side, content creators can embed a single movie into a web page that automatically senses the client's connection speed, and plays back the movie with the appropriate data rate. This way, clients connected with a 28.8 kbps modems don't have to wait for long downloads of high-bandwidth movies (or stream movies that would exceed the available bandwidth). At the same time, clients with faster connections can view higher quality movies.
To take advantage of this feature, you first need to export movies for different internet connection speeds. You can do this with QuickTime Player Pro and other QuickTime based programs. For each movie, you can adjust many aspects of the file in order to make it smaller for slower connection rates (such as movie size, codec, data rates, frames per second, etc.). When you have created the multiple versions of your movie, you need to create what is called a "reference movie." The reference movie acts like an "alias" in many respects--it basically serves as a pointer to the different movie files you have created.
Figure 2 , Example reference tree
To create a reference movie, you need a tool, such as Media Cleaner, or Apple's MakeRefMovie application. For more information on these and other QuickTime authoring tools, see http://www.apple.com/quicktime/authoring/ .
Finally, put the movie files on your server, and then embed the single reference movie into your web page and the QuickTime plug-in will automatically handle the rest.