Streaming Video, an Overview:

The Streaming Solution:

Streaming multimedia has several advantages over downloaded: It can be embedded in a web page and mixed with text, graphics, and other video. There are two main categories of streaming multimedia on the web:

progressive download/HTTP streaming.
real time streaming protocol (RTSP).

 

Progressive Download/HTTP streaming:

Progressive download of video files does NOT require a streaming server. Progressive download files can be embedded into a web page or played in a new player window. Embedding the files is nice because they can be accompanied by text and graphics.

Benefits of HTTP streaming:

Lower server cost: HTTP streaming files are handled by the same protocols that handle text, audio, and graphics information. You do need the right plug-in installed (RealVideo, QuickTime, and Windows Media Player are the standards), but you can stream the videos from the same web server the rest of your site is on.

Higher quality: All of the above standard formats will buffer before play-back. This means that the plug-in downloads enough stream before play-back so there will be a continuous play at the available conection speed. So if the video is downloading at 56 kbs and a 30 second video is compressed to play at 112kbs, the video player will pause until it has downloaded half of the video before beginning the play. Once it starts playing, it will continue to download the end of the video while it plays through what's be collected.

This makes HTTP streaming a great way to show commercials, short films, greetings and other movies less than about 10 minutes in length.

Problems with Progressive download/HTTP streaming:

Not suitable for large files: There are two reasons progressive download files are unsuited for long-form movies:

1) Because they are downloaded to the viewer's computer, video files over 50MB (~10 minutes at 200kbs) may cause viewer's computers to run out of hard drive space and crash.

2). A client cannot navigate to the end of a long movie until it has been entirely downloaded.

Not suitable for live broadcasts: HTTP streaming only transports terminated files, not open-ended flows of data.

 

Real Time Streaming Protocol:

Content producers may solve the three problems above by using RTSP to deliver their files. RTSP files can be very long without filling up the client's hard drive. RTSP streaming requires a Streaming Server that pushes the file to the client's player. At no time is the entire file ever downloaded and cached or stored locally on the client machine, instead just the frames of the video that the viewer is seeing (with a few frames ahead) are delivered. The video is rendered and played in real-time as the data comes in over the network directly from the streaming server.

Some advantages of RTSP include:

Ability to provide a "live" broadcast: (this can be either live webcasted video of an event as it is going on, or the 'live' webcast of a television station's regular programming.

The media file is protected: Since the file remains on the server it cannot be saved to the local drive on the client machine (it can however, be recorded in other ways).

Navigation of long videos: For a long clip, the user doesn't have to wait for the entire first portion of the clip to download first. They can instantly "thumb" to the end of the clip and resume play from there.

Problems with RTSP:

RTSP Requires a specialized server. Whereas the other forms of media delivery use standard HTTP or ftp to send files, and works from any standard web server, RTSP media requires a specialized server. This server is constantly talking to the client stations to determine what part of the movie they have requested, what the network status is, etc. RTSP servers come in several flavors, the dominant ones being Real Video Server, QuickTime Streaming Server, and Windows Media Server.

Lower quality than HTTP streaming: For streaming to a 56k audience, the movie should be authored at ~40kbs, as 56k modems rarely perform at their peak speed. With progressive download, if the client's bandwidth drops below the data rate of the movie, the movie pauses until the client catches up, and as noted if the audience is patient, the video can be authored at a higher speed and quality than the viewer's modem. With RTSP when the client's bandwidth falls below the rate of the stream, the server scales back the stream by dropping frames, then video altogether. Thus the movie must be authored at the minimum likely connection speed of the audience.

Network congestion: With HTTP streaming, network congestion causes the video to stop. When enough of the video has been buffered, the video starts playing again. While this is also true for non-live RTSP streamed videos, for live RTSP streams, the viewer will miss video during periods of network congestion.