Streaming Media Concepts

The delivery of information content through Windows Media technologies is composed of the following processes:

• Capturing
• Encoding
• Distributing
• Delivering
• Playing

The following sections describe some basic streaming-media concepts, and provide a foundation for designing a complete executive-broadcast solution.

Difference between Downloading and Streaming

There are differences between downloading and streaming content. When a download is complete, a copy of the original file is safely stored somewhere on the computer's hard disk, while the original file remains in its original location.
Downloading a multimedia file results in the same outcome however, after the file has been copied to the hard disk, you can open and play the copy by using a player application such as Windows Media Player.

The main advantage of downloading is that the downloaded file can be of any type: music file, text file, bitmap, and so on. A disadvantage is that downloading files takes time, and you have to wait for all of the data to be copied from the server to your hard disk before you can play or view the file.

With streaming content, you get instant gratification€”there is no download wait. Content is played as it is received from a server over a network, and is not saved to your hard disk. Instead of waiting for an entire file to be copied, your player application plays it as soon as the first chunk of video arrives. Streaming also enables you to do live broadcasting, just like a radio or television station, except the broadcast is over the Internet.
Streaming content does have disadvantages. Real-time playback of audio and video is highly dependent on the bit rate of the content, and the available network bandwidth that delivers the stream.
Bit Rate and Bandwidth

For streaming to work properly, the player application must play the audio and video content at a steady and continuous rate. If the stream is not continuous, the picture and sound will either stop or play back unevenly. This uneven playback occurs when the content is streamed at a bit rate that is higher than the bandwidth available on the network.

The amount of time needed to download the file is directly related to the size of the file, the available bandwidth of the network, and the speed of your modem or network interface card.

When preparing content for streaming over the Internet€”a process called encoding€”it is important to consider the bandwidth that is available to the people who will be playing the stream, and then select a bit rate that is appropriate for that bandwidth.

Live and On-demand Content

Two delivery options are possible when streaming: live and on-demand content. Live content is often used when viewers want to see and hear an important event as it is occurring. Examples might be a class lecture, presidential election, a farewell performance by a beloved singer, breaking news, or a high-profile sporting event.

Streaming on-demand content is the appropriate choice for times when the message is not time-critical. This delivery option enables you to re-broadcast a live event to users who missed it the first time. They can request the stream when they want to watch it, and can control the playback to meet their needs.

If you intend to stream live events, you must ensure that you have appropriate infrastructure in place to support the stream. This infrastructure includes encoders to compress the content, enough bandwidth to accommodate all concurrent stream requests, and multiple servers to distribute the load and to provide redundancy if a server fails. On networks where it is possible, it may be useful to install routers that have been configured to support a special kind of broadcast called multicast.

On-demand streaming has potentially lower bandwidth requirements because you are not required to service hundreds (or thousands) of concurrent streams.