The actual difference is that media players can start to show the video while it’s downloading and install. For instance, a FLV documents being supplied via HTTP Progressive download will start to play in your Flash Gamer as soon as a little bit of data is received by the browser. The very same holds true for Windows Media documents. Quick Time will wait until the entire file is downloaded and install prior to it plays, unless the QuickTime gamer on the PC/Mac is established for modern play. So be cautious when publishing QuickTime videos.