A couple years ago I created a quick proof of concept to different aspects of putting together a package to handle key frame based animations much like you can do with tools like After Effects and HitFilm. It has basic support for assets, footage, layers, and compositions along with linear, Bezier, ellipse, and spline (incomplete) path interpolation.
The code is fairly rudimentary and a bit incomplete but I figured someone else might find it useful. Since it was created as a PoC there are quite a few things that could be done a lot more effectively if some time was spent sanitizing it a bit more. Iv'e attached a snapshot of the source in case anyone is interested.
Sample playback:
Some general details.
Project files are for VS2017.
Built and tested on SFML 2.4.2 (should work on 2.5)
SFML library should be dropped into externals/SFML or change the solution macro SFMLDir to point to the location containing your copy of SFML.
Build with modern C++.
Includes test/examples.
Intended more for authoring content. Playback in games would be handled a bit more efficiently.
Modeled after concepts common in applications in HitFilm and Adobe After Effects.
Includes bugs so there's no need to buy your own.
Emjoy!
I'll push this to GitHub when I get some free time.