Monday, June 2, 2008

Film production tips #6: Digital encoding tips

Recently I've been plagued by an annoying "pop" in brightness in the above scene that only appears in the divx compressed video and is completely absent from the lossless source shot (after careful frame by frame examination.) This shot is longer than most of my shots, so I got curious and measured where the pop occurs from the preceding scene. Turns out it's at frame 300 (more or less)

Now the divx codec has a setting for maximum keyframe interval, the default is 300 frames. So every 300 frames, the codec is going to 'refresh' the stream by inserting a new keyframe. Without getting too techincal, this creates a dual frame visual discrepancy which is visible to the human occular visual eyeballs type situation scenario.


So in simple terms, you should set the max keyframe interval to the length of the longest shot in your composition, in order to avoid 'popping'

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