Dupped() - yet another frame duplication function

[Corran]

There is a big difference though between rebuilding a frame from the last keyframe in say divx and requesting a null frame via lagarith. With the later, all it has to do is reference the frame that is going to duplicated and feed it to the app requesting it. It should maintain it's frame accuracy in that process. As far as the editing app is concerned, it is seeing a video from the lagarith decoder that is all keyframes.