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Compression keyframes are different from the keyframes
that you use to control track or clip properties, such as audio
volume or clip rotation. Compression keyframes are automatically
placed during export at regular intervals in the movie. During compression,
they are stored as complete frames. The frames between the keyframes,
called intermediate frames, are compared to the previous frame and
only the changed data is stored. This process can greatly reduce
file size, depending on the spacing of the keyframes.
Choosing an optimal compression setting is a balancing act that
varies depending on the type of video material, the target delivery
format, and the intended audience. Fewer keyframes and more intermediate
frames result in smaller file sizes but produce lower-quality images
and motion. More keyframes and fewer intermediate frames result
in larger file sizes but produce higher-quality images and motion.
Often, the optimal compression setting is arrived at through trial
and error.
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