Created attachment 164047 [details] Adobe After Effects Manual SUMMARY *** When setting keyframe interpolation, the concept of what is considered "In" and what "Out" is wrong, in the current implementation. In: is when the time is "coming in" to the selected keyframe. Out: is when time is "going out" of the selected keyframe. *** ADDITIONAL INFORMATION There are a lot of references to this, but the main ones should probably be Adobe products (After Effects / Premiere Pro) and OpenToonz, all of the using the concept in the right way. A lot of classic animation related textbooks where the concept is explained clearly: Animator's Survival Kit, etc. Here you can see a demo of After Effects Easing In/Out into play: https://www.youtube.com/watch?v=UVox_2py9yU Below I will attach excerpts from the After Effects manual and from Animator's Survival Kit by Richard Williams, explaining the concept.
Created attachment 164048 [details] Screenshot from Animator's Survival Kit, a well known and respected classic animation textbook.
Also (and more relevant to potential Kdenlive potential users expectations) Premiere Pro uses this concept in the same way as After Effects. Here you can see someone explaining how to use it in Premiere Pro (and airing his previous own confusion about it) https://youtu.be/vupwCdFgWpE?t=200 (the video goes directly to the moment he talks about it) By the way, Blender is currently using this concept in the wrong (inverted) way.
Another program that uses the In/Out concepts correctly is OpenToonz (Studio Ghibli's open source animation software) Here's a quick video I made showing it in action. https://youtube.com/shorts/FufHca0xjow
Created attachment 164052 [details] OpenToonz ease in/out The OpenToonz Youtube video looks terrible, so here I've uploaded de same video.