This chapter covers the types of video that RealSystem can stream. It will help you decide whether to convert your video source file to RealVideo or stream from another video format. It also provides tips for capturing high quality video.
Because video loses image quality when compressed, you need to start with high quality video source. This section gives you tips on which video source formats to use, as well as pointers on staging, shooting, and digitizing the video. Although geared for RealVideo, these guidelines will help you no matter what video format you choose.
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Additional Information |
For pointers on producing audio, see "Recording High Quality Audio". |
Observe the points below if you intend to shoot a new video rather than use existing content. These guidelines will help you produce high-quality video with a low compressed file size.
To reach Web users with 28.8 Kbps modems, you need to produce a small video, such as 176 x 144 pixels. If you show an instructor pointing to a chart, for example, you may need to zoom in on the chart to make the text legible.
The less that changes from frame to frame, the more the video file will compress. Most compression technologies reuse existing data when frames are similar. So a video with relatively stationary subjects ("talking heads") will compress more than a music video with rapid scene changes and a lot of movement. You can do the following to cut down on unnecessary movement:
Of course, you don't want to eliminate all dynamic elements! When you do include rapid movement, give enough time for objects to resolve. Because of low frame rates and high compression, objects coming to a rest may appear blurry at first. If you have a dialog box popping up on a computer screen, for example, show that box stationary for a few seconds so that the image resolves.
Bright lighting at a constant exposure keeps the foreground detail crisp and cuts down the compressed file size. Use uniform, light colors in backgrounds and clothing. Dark colors and complex textures such as paislies and stripes add to the file size. They can also degrade the video with unwanted visual effects.
Keep the following points in mind when digitizing a video source.
Whether you shoot a video yourself or digitize existing material, it's important to use a high-quality video format. The following are common video formats in order of descending quality:
Video playback devices commonly have two output types, S-video and composite. Use S-video, which generally produces better results.
If possible, digitize in an uncompressed format. This gives you greater flexibility when editing the video. It produces larger source files, however.
RealNetworks introduced RealVideo with RealSystem 4.0. A RealVideo file uses the file extension .rm and typically includes a soundtrack encoded in RealAudio.
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Additional Information |
For more on RealAudio, see "Producing RealAudio". |
RealVideo is a compressed format, so you typically start with a digitized, uncompressed format such as AVI. You then convert this file to RealVideo for streaming. Check your encoding tool's supported input formats, which should be some or all of the following:
You can typically convert compressed or uncompressed AVI to RealVideo. RealNetworks recommends using the uncompressed format whenever possible.
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Additional Information |
See "RealNetworks Encoding Tools" for more on RealVideo encoding tools available from RealNetworks. |
Like RealAudio, RealVideo uses a "lossy" compression scheme that discards parts of the source file during encoding. When you encode RealVideo, you simply choose an encoded video bandwidth from the encoding tool's list of supported bandwidths. You also choose a RealAudio Codec for the audio track.
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Additional Information |
See "Using RealAudio Codecs" for general information on Codecs. |
RealSystem can stream other video file formats in addition to RealVideo. Because these file formats may not be as highly compressed as RealVideo, they may not work well with low bandwidth connections. The following sections give you guidelines for steaming these other video formats. This information will help you decide if you should stream the native format or convert the file to RealVideo.
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Note |
The following sections will be added later. |