Web delivery (http) from a Web server or podcasting server does not take advantage of streaming. Many people think they are streaming when they are just making a file available for download, but this is okay as long as they know what can happen with their file.
In the case of delivery from a web server, the movie is downloaded to the user's computer, and the movie begins to play as soon as enough of the movie is downloaded. The movie continues to download while it plays. If all works well, the downloading stays ahead of the playing. If the movie catches up to the downloading, the movie stops while the download continues. The movie may or may not be available for later viewing on the computer depending upon how the computer is configured.
This is an example of a http delivered movie.
When using a podcasting server, the movie downloads to the user's computer completely before playing, and is available for the user until he or she deletes it. The movie is then played on a computer or portable device like an iPod. In addition, podcasting servers create newsfeeds that allows a user to subscribe using software on his or her own computer. This makes it simple to keep up with the subscribed sites as the computer does the drudgery of checking to see if anything new has been put up. If new material is posted to the podcasting server, the user's computer automatically downloads it, and can automatically transfer the download to a portable device. Sweet!
Streaming delivery (rtsp) allows users to view longer movies that would take too long to download before playing. Streaming buffers a short amount of the file before it starts playing.
This is an example of a rtsp delivered movie.