Streaming Media: 5
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Selecting the Appropriate Content for Streaming
One of the first things you need to do when creating streaming media content is to decide which bandwidth(s) you are going to target. Low bandwidth (such as a 28.8 Kbps modem) is not suitable for content with a lot of motion in it, such as a sports event. Trying to stream a soccer match over such a low-speed connection would result in a tiny window (160 x 112 or 176 x 144) with miniscule players. Video interviews with individual sports stars, on the other hand, would give perfectly acceptable quality over a 28.8-Kbps connection.
The following table shows what you can expect your audience to be able to view at various bandwidth levels. Note that the bandwidth speeds are given in bits/second, not bytes/second:
| Network | Bandwidth | Target Data Rate (Usable Bandwidth) | Capabilities |
|---|---|---|---|
| 14.4 Kbps | 14,400 bps | 9,600 bps | Compressed audio, script commands, markers, URL flips |
| 28.8 Kbps | 28,000 bps | Less than 24,000 bps | (all above) small frame, still images, low frame rate, highly compressed video, compressed audio |
| 56.6 Kbps - 128 Kbps, ISDN | 56,000 bps | ~53,000 bps (all above) | compressed stereo audio, compressed video, faster frame rates, larger frame sizes |
| Intranet | 110,000+ bps | ~100,000 bps | (all above) larger and faster video, higher-quality audio |
| Fast Network | ~210,000+ bps | ~190,000+ bps | (all above) uncompressed audio |
| T1 | 1.544 Mbps | (all above) uncompressed stereo audio | |
| T3 | 40.144 Mbps | (all above) uncompressed video |
There are some key factors you can play with so that your content will fit within a certain amount of bandwidth:
- Frame size. The bigger the image size in pixels, the more bandwidth it will take for the content to play. In order to keep the picture size large, you will need to sacrifice some of the other factors in this list.
- Frame rate. The higher the frame rate, the more bandwidth it will take to play back the content. In order to keep the frame rate high, you will need to sacrifice frame size, picture quality, and/or number of colors.
- Picture quality. The higher the picture quality, the more bandwidth it will take to play back the content. In order to keep the picture quality high, you will need to sacrifice frame size, frame rate, and/or number of colors.
- Number of colors. Sometimes you will find that limiting the palette of colors you choose from in creating content will help conserve bandwidth. If you want to maintain bright, rich colors, though, you will need to adjust the above factors to fit the content over low bandwidths.
Many of the streaming environments today offer built-in effects and transitions. For example, the animation provided by Macromedia Flash uses the processing power of the viewer's computer to create movement and typically doesn't cause an impact on the bandwidth needs of the stream.
Bandwidth Examples
Selecting too small a bandwidth for the amount of data you are streaming has a significant impact on the quality of the video. To illustrate this point, these examples illustrates the reult of compressing the same video clip for the three most popular media players at two very different bandwidths.