Streaming Video
Video types (vis-a-vis "formats")
Standard - used on computers or as files to be used to produce a DVD. These files are large - especially the ones that are purposed to play with high quality full screen.
Streaming - used on the web.
The main difference here is not size, but what it takes to play the file.
If you were to upload a standard file of your video, your user would have to wait - and wait - event with broadband internet connection until the entire file downloaded to your user's computer.
Streaming speeds things up - at least if your web user has broadband. When your user opens the web page with an embedded video it "calls" your video to start downloading to the computer of your user.
When a minimum of the file has been downloaded to your user's computer, the video starts to play. It continues to download to a "buffer" as your user plays the video. As long as your internet connection keeps downloading the file behind the scenes, the video plays without interruption. If the connection is cut off or slows down, the video may pause until the "buffer" has enough video information to allow the user to play the video.
The user doesn't have to wait for the entire file.
There are different streaming rates, the higher the number the higher the quality. A 256K stream (good quality for medium (3 - 10 minute) clips) will look and sound better than a 128K stream.
Yet, the higher the number, the longer the wait before the video starts to play. The higher the quality the more likely your video will pause to rebuild the buffer from time to time.