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Old 23 May 2002, 06:40 AM   #1
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Default Encoding for reverse playback

Is there something that must be set in the DIVX codec to provide for reverse play of the movie? I want to be able to do reverse and fast reverse but when playing in WMP the buttons are disabled.
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Old 23 May 2002, 10:44 AM   #2
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Sorry, due to the structure of divx video, reverse playback is extremely difficult.

Divx and most other high compression video formats, use so called partial frames, these frames depend on at least one other frame (usually the frame just before it).
This means that, to display a randomly chosen frame (number n), you first need to decode frame number n-1, and before you can decode that you must decode number n-2 and so on . . . untill you hit an key frame, which can be decoded independently of other frames.

In theory, reverse playback can be achived, using caching of at least m frames, where m is the maximun keyframe interval, I don't have a clue if any players can do this.

An easy way to do fast reverse, would be to only display the key frames, but as you said, wmp does'nt support this with divx files. I don't have a clue what other players might actually have support for this.

I don't think there is anyway you can get wmp to do what you want.

To make reverse play back easier, you might set the maximum key frame interval to 1. This way the file is just as easy to read backwards as forwards. But again I don't have a clue what players might support this. And ofcause this is extremely inefficient.
Donate your idle CPU time for something usefull.

Last edited by khp; 23 May 2002 at 10:49 AM
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