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This is used to decrease the frame rate of a video. Changing the frame rate means eliminating a frame for any given number of frames (1inN); but if frames that are important for visual continuity are deleted, temporal artifacts arise: flickering, slowdowns, accelerations, etc. The Decimate filter maintains a higher quality because it first eliminates duplicate frames or frames that are most similar, thus limiting the appearance of artifacts. It is often used after the Invert Telecine plugin to make the video more smooth.
One use of the decimate effect can be applied to a DVD to convert the 29.97 fps video to the 23.97 fps film rate, but the effect can take any input rate and convert it to any lower output rate. The output rate of decimate is the project frame rate. The input rate is set in the decimate user interface. To convert 29.97 fps progressive video to 23.97 fps film, apply a decimate effect to the track. Set the decimate input rate to 29.97 and the project rate to 23.97.
Keep in mind that every effect layered before decimate, processes video at the decimate input rate and every effect layered after decimate, processes video at the project frame rate. Computationally intensive effects should come below decimate.
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