I found a website called Plask. (an .ai website?) You can upload a character with a basic rig, and the webpage will allow you to take video from your webcam and extract the motion.
They have 4 different objects already in their web library, but if you upload one, they have a retargeting page where you can tell the bones in the object to correspond with their ai setup. I tried to upload the Udim Monster from blender demo scenes, and although it showed up in the screen, even with the keyframed animation, I couldn't get the bones retargeting to work. Maybe I missed a bone?
With the object, (a knight) provided, I recorded myself swinging my arms in my living room, with a background of a typical house, (even with a fish tank) and the ai picked up the motion with a high degree of acuracy. My idea was to have the character hit a chair.
I was able to export as an fbx, and import that into the classroom demo scene in blender. I was able to select all the keyframes and use control O to smooth the keys in the graph editor. (Without that step the animation was a little jittery.)
Then I tried to use rigid body dynamics, (in theory to make the character hit a chair) But in this scene the chairs arn't available to the rigid simulation. (That was werid) So I keyframed one of the chairs hitting the wall and bouncing off. I just lined up the motion captured swinging arm to around the right frame and moved the chair accordingly.
I might try a similar scene and see if I can do a simulation too.
I think the site which at the time of this post is free, an example of tech that could if further refined, make motion capture easy.
They provided examples of people in bright colors with a green or blue screen. So, if trying this site, helps to take your footage like that.
The whole process took about 1/2 hour.
One confusing thing was that after I captured and extracted the motion, it shows up in the library section on the left. It took awhile to see how to apply the motion. You drag the motion to the character in the library.
So I tried the website again, this time with a sitting motion. The hands went through the lap, so I made a second where I kept the hands above the lap. (the character on the right)
This import of the fbx file, I made a collection and stuck that in there. I noticed some weird movement from the mocap in which the character was moving up in the y axis. So I was able to goto pose mode select the hip bone, and add in a limit modifier for a specific range of frames, and clamped that. So when the charcter sits in the chair he doesn't float up. So I've never used mocap before and learning the Graph editor is going to help in getting these characters to just sit in a chair. In this iteration, the character on the right has his feet clipping in the sofa. And the characters hands pass through the legs. I started to try to keyframe the arm bone so that doesn't happen, but there's a learning curve to that too. I installed an add on called anim aid, that I think might help with cleaning up the mocap data. If you move a bone, anim aid will move all the keyframes of the bone afterward. This mocap site might be great for previs stuff. Was very fast to capture and import their character. Importing your own character and retargeting the bones... I couldn't get that to work so well.
The below video shows you how to retarget Your motion to a character with a t-pose using the copy constraint. He also shows how to clean up motion capture.
You have to select each bone and add the constraint, but he lists a free plugin that automates this tedious task. :)
This person has some good ideas about real mocap capturing:
A person named mark has some tips about cleaning up the mocap data. He uses the alt o for smooth and clean keys and deletes keyframes that are out of place causing as he calls that janky animation.
Royal skies is a favorite of mine, His tutorials are quick and to the point. He talks about his workflow for cleaning up mocap data. My brother mentioned in the first little animation above where the guy swings his arms, the feet are shuffling. Royal skies, recommends making a keyframe in the timeline where the feet are on the floor. Then find the points where they arn't and move the character down or up. He goes on to say he makes keyframes on the major poses, and adds in poses for hands at certain points because mocap doesn't do hands and fingers well. (A good rig might).
And this video shows how to import your mocap data using the rokoko app, which looks really easy to work with.
This person talks about how to get your mocap onto your character and how to use the non linear editor and graph editor to make changes to the motions. The last part of the tutorial explains how to add keyframes without modifying the original mocap. (tweaking the bones.)
He also talks about selecting the bones you want to animate and how to keyframe them to fix issues like the hand going through the forearm etc.