For rendering, Slate is using a library from GitHub called FrameCapturer. MP4 recording was not behaving correctly at that time, and this is the reason I decided to deprecate it. I see though, that the library has recently been updated, which is a good thing of course. I will test the MP4 recording capabilities of the library out again and see if it now works better that it did before. If so I will add mp4 again! 🙂
one quick extra question regarding tweening. It is not possible to set easing options for animating property values? only transform action clips have easing options correct?
Tweening options are not available in animate property values (or any other keyframe based parameters), because in animate property values, there is a full curve editor with which you can basically define any type of tween/interpolation you want and is at your total control 🙂
So for example something like this, would be the equivalent of BounceInOut.