acs
commented
1 year ago «The animations were created at Mixamo using motion capture and cleaned up by key frame animators. All its animations work with characters created in Fuse and/or rigged with Mixamo's AutoRigger.»
We need to translate the data motion captured into the rigs (bones) of the model.
https://en.wikipedia.org/wiki/Motion_capture
This kind of animation is based on capturing the movements from real life scenes, mainly characters.
The motion data is captured using different devices with sensors. And this data is translated to the bones of the model for its animation. This is how Mixamo works. One issue with Mocap is the quality of the data captured and its translation to animations.
There are two Open Source projects in this field: https://freemocap.org/ and https://chordata.cc/