Last Updated on Wednesday, April 25, 2012 at 7:32 AM
Progressive Download Versus Real-time Streaming
Progressive download allows users to watch or listen to media as it is being downloaded from a standard web server to their hard drive. This method works best for short-form media where file size is limited. Progressive download ensures high-quality playback regardless of users' Internet connection speed, although users with slower connections will wait longer before media starts to play.
Real-time streaming uses a specialized web server such as the QuickTime Streaming Server or the Windows Media Server to deliver media in real time over the Internet. Streaming takes into account the users Internet connection and delivers the most appropriate media file to insure the best quality of service. With the open standard Real-Time Transport Protocol/Real-Time Streaming Protocol (RTP/RTSP), no file is ever downloaded to a viewer's hard drive. Media is played, but not stored. Naturally the image size or frame rate will vary as the video is delivered at various internet speeds, from slow dial-up to broadband. Real-time streaming is often preferable to progressive download for webcasts of live events, delivery of long-form video, and 24/7 Internet radio and TV channels.
Streaming Types
Unicast streams are simple one-to-one streams, like a phone call from the server to a single client computer. To reach many clients, the server must send many streams, which is a less efficient use of bandwidth. However, each viewer of a unicast stream can randomly access the movie, playing only the parts they want to see. Typically, unicast is used to stream prerecorded movies.
Multicast streams are sent directly to a group address, such as an IP multicast address, which in turn can be simultaneously accessed by many client computers. The viewer of a multicast has no control over what is presented. Multicasts are an efficient way to deliver the same material to a group of people over a LAN, as only one copy of the stream is sent over the network.
Reflected multicast streams take live media from another source, such as a radio or TV broadcast, and stream it out to viewers as a series of unicasts. This is the approach taken by online news networks, such as CNN.com.