Nicholas Frechette's Blog Raw bits
In order to keep the material concrete, we will take a deeper look at some popular video game engines. We will highlight the techniques that they use for character animation compression and where they shine or come short.
Unless you use the curves directly authored by the animator for your animation clip, the animation compression you use will end up being lossy in nature and some amount of fidelity will be lost (possibly visible to the naked eye or not). To combat the loss of accuracy, three error compensation techniques emerged over the years to help push the memory footprint further down while keeping the visual results acceptable: in-place correction, additive correction, and inverse kinematic correction.
Signal processing algorithm variants come in many forms but the most common and popular approach is to use Wavelets. Having utilized this method for all character animation clips on all supported platforms for Thief (2014) I have a fair amount to share with you.
Curve fitting builds on what we last saw with linear key reduction. With it, we saw that we leveraged linear interpolation to remove keys that could easily be predicted. Curve fitting archives the same feat by using a different interpolation method: a spline function.
With simple key quantization, if we needed to sample a certain time T for which we did not have a key (e.g. in between two existing keys), we linearly interpolated between the two.