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351 ADOBE PREMIERE 5.0
User Guide
presses video relatively quickly, making it useful for video files that must play well on both
high- and low-end computers, but to achieve this it requires more time when compressing.
Symmetry varies depending on the codec and is generally not adjustable within a codec.
Recompressing clips
When you play back or export a program consisting of compressed source clips, you can choose
to recompress source clips that are already compressed or to leave them as they are. It’s usually
best to avoid recompressing the clips, because you cannot save additional space by compressing
them again at the same settings. In fact, because many compressors are lossy, recompressing a
clip degrades picture quality.
Premiere attempts to avoid recompressing when frames appear to be unchanged from the
corresponding frames in the source clip, but there are situations where source clips must be
recompressed. In general, recompressing is necessary when you’ve applied edits, effects, or
output settings that cause significant changes to frames in a clip, such as the following:
•
Reducing the Quality or Data Rate settings
•
Changing the frame rate, color bit depth, keyframe settings, Special Processing options,
codec or codec options, and in most cases changing the video type
•
Changing the visual content, including frame size, transitions, filters, motion, transparency,
field options, frame hold, or frame blending
Selecting the Always Recompress option will always recompress clips regardless of whether
or not frames changed. For information on setting recompression options for playback,
see “Video settings” on page 61; for export, see “Setting the data rate” on page 300.
Other factors that affect file size
Some video characteristics can affect the size of a video file whether compression is applied
or not, and regardless of the codec you specify.
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