Animation system: mesh selection errors

[culacant]

Most game objects have their animation frames split over different files, eg the CYRSA000-023 3DC files split all cyrus animations into 23 different files.
The animation control frame data does not take this into account, it gives frame numbers starting from 0 for CYRSA000 frame 0, up to frame 500-something for CYRSA023 frame X.

It is not possible to put all the 3DC frames in a single unity blendshape, since some of the files have different vertexcounts and this is not supported in blendshapes.

Currently, we switch the "active" file for an animated object when we detect the frame number is outside the current 3DC mesh. We then find the file where this frame number is located in and put that in the current blendshape.

However, when doing this 3DC mesh switch, we always get (at least) a single out-of-file frame, resulting in an error and a T-pose.

Desired implementation is a smooth switching between 3DC files, so no errors or T-poses occur during animation switching.
Bonus points for figuring out how to do inter-frame interpolation in this case, since we cannot interpolate between different meshes.