I don’t think there is a direct “free” pathway here.
As a studio, we spent a lot of money on several Rokoko suit, but as much as I would like to there is just no way I could ever reccomend anyone spend that kind of money (now even more as they sent out a mailer that prices are increasing) for such a low quality end result.
An indy studio is definitely 100% better off spending the 2 or 3 k needed to book a proper recording session at a proper mocap studio.
In fact, they propbably end up saving on time and money.
And get a much better end result in the end. Mocap studios have 2 things you don’t: experts or people with hands on experience that can fix up most things by just looking at a rig, and the proper tools needed to get you the final fbx…
Back to doing it yourself…
We record perfomances in engine, extract to Blender acrually, just because of BoneBreaker (addon we created specifically to work with unreal), edit and fix them up, and then import into the final project.
This is done via rokokolive and unreal face, both of which use the livelink plugin to communicate with the engine over the network.
There is a bit of delay between the actor and the recording on the unreal side.
You have to have your assets ready to go to film properly. Particularly the actor face morph targets need to be created specifically to match the actor’s maximum range of motion.
The process for that is rather grueling, about 4 days of work between rigging the face and creating the poses, assuming you remebered to have the actor do all the needed poses so that you can mimic the final poses.
Tweaking facial expressions after the fact is generally not a good idea.
Best you can do is make them more fluid by removing keyframes between the minimum and maximum values so as to have really clean exports (since they are curves, and our ue4Curve tools does still work, you can re-export from blender without having them keyframed at every frame, peoviding a generally better end result).
Tweaking bone positions after the fact is rather standard, you rig the animation (again, we use are tools for it) and you mess with it to your hart’s content.
This too generally just involves removing hard keyframes to improve fluidity.
Definitely a lot of tweaking for things that the rokoko suit fails at - touching yourself, touching your head/face, touching a specific target, being in a specific x/y/z location for syncs, finger positions, awkward bone rotations due to the sensors sliding around during the takes… etc.
Yes, in theory you can bring it all back in engine, apply it to a metahuman, and use the control rig stuff to tweak parts - I surely never even thought about doing it, but i do suppose that’s an option (if you want to ruin a good thing you put hours into :P).
That’s all i got.
TL:DR;
Spend $2k on a mocap studio, save yourself 2 years of work.
Ps: didn’t bother proofreading it… maybe later i will…