About Video Compression - Adobe PREMIERE 5 User Manual

348 APPENDIX B
Compressing Video and Audio
When playing back the Timeline to record on videotape, preserve the highest quality by
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specifying the same compression settings you used to capture the source. If the video in your
project was not captured using your computer, specify the highest quality compression settings
your computer can handle while still playing back video smoothly. You specify compression
settings for Timeline playback in the Video Settings and Keyframe and Rendering Options
dialog boxes.
When exporting video to a file, use compression settings that play smoothly on the kind
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of computer system you expect your audience to use. For media such as the World Wide
Web, it may be necessary to specify lower quality settings to minimize the data rate of the
video. You specify compression settings for export in the Export Settings and Keyframe and
Rendering dialog boxes (see "Specifying compression for final video" on page 298).
Applying the best compression settings can be tricky. Your goal is to apply the degree of
compression that lets the clip stay within—but not too far below—the target data rate. If you
apply too little compression, the data rate will be too high for the system, causing errors such
as dropped frames. If you apply too much compression, lowering the data rate too far, you
won't be taking advantage of the full capacity of the system and the picture quality may
suffer unnecessarily. You can use the Data Rate Analyzer to evaluate any video file; see
"Analyzing clip properties and data rate" on page 127.

About video compression

The topics in this section cover video codecs and some of the techniques they use to handle
various situations. Understanding these techniques can help you identify issues and priorities
as you evaluate compression strategies for your projects.
Spatial compression
Spatial (space) compression compacts the description of the visual area of a video frame by
looking for patterns and repetition among pixels. For example, in a picture that includes a blue
sky, spatial compression will notice that many of the sky pixels are a similar shade of blue.
Instead of describing each of several thousand pixels, spatial compression can record a much
shorter description, such as "All the pixels in this area are light blue." Run-length encoding is