1 Topic by drewread

  • drewread
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While scrubbing through videos initially to mark and note areas of the video for further examination it would be really nice to have a button to play the video in reverse. Stepping back frame by frame is great for fine tuning, but to go back and find a moment that just passed would be easier with a reverse play button.

Drew Read

2 Reply by joan

  • joan
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Yeah backward playback (and even stepping) is surprisingly complicated. The issue is that most video codecs are optimized for forward playback and the content of a given image is an incremental update over the previous keyframe. So to display a past frame we usually need to go way back, an unknown amount of frames, to find that keyframe, and then decode forward until we find the target frame to show.

At the moment there are a few strategies in Kinovea to alleviate this: 1. Use a intra-frame codec only by default for anything saved by the program. This makes it easier to later step backward/forward as every frame is a keyframe. 2. Keep a small cache of images in memory while playing forward, frames both before and after the current point. This way we can at least go back a few images without seeking. This also helps with smoothing forward playback at normal speed. 3. When the working zone fits entirely in memory, all the frames are cached, this makes random access fast again. In fact if you do this you will see the menu Video > Reverse is active and you can switch the entire video to backward playback.