Kdenlive/Development/Ideas/Speed Change

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Speed Change

Speed effects are different from other effects in that they alter the length of a clip. This puts speed effect into a separate effect category.

There are different challenges that arise with speed change.

When slowing down, intermediate frames are needed. This is done e.g. by slowmoVideo using optical flow.
When speeding up, motion blur may be desired to keep the image look natural
Audio also changes. Is it simply stretched, whereby pitch changes as well, or should only the speed change (but not pitch) as done e.g. by Paulstretch?

Editing also poses challenges:

It is impossible to edit inside the timeline due to the clip length change
When allowing curves for speed change, the effect GUI becomes much more complex and does not fit into a widget anymore. slowmoVideo has an own UI just for that with a 2D canvas. The input video is on one axis and the output video on another axis, and a curve defines which frames the output video picks from the input video.