Just a few details on fixing feet sliding/sinking for motions which cannot be effectively fixed with Motion Correction.
I hope someone find it interesting and/or introduce their own alternative methods or tips to improve the workflow.
Mid to advanced experience level with animating on the timeline required.
It's not actually "fixing", but rather
recreating motions for 4 bones - L/R Foot and L/R ToeBase.
The idea is to have 2 characters with the same motion at the same location in the project.
You then animate 4 mentioned bones of one character without sliding while having second character as a reference for planting feet.
During the process you would want to hide/un-hide reference character to have a clear view of the main character you are trying to fix the motion for.
Animating L/R Foot
You do not actually animate bones. You do it by animating Reach Targets attached to L/R Foot nodes.
So you have to create 2 reach targets, place them on the timeline and start animating to have feet of the target character follow the feet of the reference character.
You select an L/R foot node and click Create Dummy in Edit Reach Target:
The biggest issue during animation is target rotation. Vast majority of human feet motions pivoted to toes.
But foot bones and consequently reach targets pivoted to heels.
So a slight turn with rotation would require repositioning reach target with move to arbitrary match initial toe position.
And mismatch with positioning even for a tiny fraction of an inch would result in sliding.
I came up with orthodox foot rotation by setting a Pivot point for Reach targets to the location of toes.
It would feel a bit unusual at first, that while rotating reach target by X the Calf and Thigh bones are pushed up. But it's a matter of getting used to.
The benefits are obvious. Once foot is rotated with reach target, the toe would firmly stay planted at the intended location with zero sliding
and further tweaking and guessing of the foot position would NOT be required. Making turns and twists would be a snap.
Here is how to make an alternative pivoting of the feet Reach Targets:
Alternative method for setting a Pivot to toes
So animating Reach targets for the feet (specially with alternative pivots) is nothing really special.
You make pose-to-pose animation moving foot from one pose on the ground to another
and fill the blanks in between (such as raising foot, rotating up/down for steps) while trying to mimic the foot movement of the reference character.
Animating L/R ToeBaseThis has to be done with character bones. As the matter of fact you only need to animate ToeBase\Rotation X.
But first, you need to remove ALL ToeBase bone animation from a given clip.
They are jittery most of the time (specially having Y and Z rotation while there has to be none by those axises).
Sample Selected parts
Then open Curve Editor, select ALL keys for the ToeBase bones and delete them.
After that, you may Flatten the clip back.
You animate ToeBase bones by X rotation where appropriate while making Reach targets pose-to-pose animation for feet.
You may animate toes afterwards when you complete Reach Targets animation for feet. In which case slight tweaking of Reach targets would most likely require in a process.
You have to use Edit Motion Layer with Edit Body Parts mode.
Try to mimic the reference character, or if toe bending is completely messed up (like in a case with boxer animation in my previous post) try to make them perform like in real life.
Keep Motion Layer clean. Do not animate anything else other than ToeBase bones.
It's very easy to lose track of that's happening at the motion layer if you start fixing other parts. You can do that later.
The only possible exception is Hip bone (Pelvis). For out of touch mocaps you may get inadequate Hip movements where it would prevent planting feet properly.
So you might have to tweak Hip bone in a way.
I found it's a good practice to cleanup unnecessary keys from timeline.
Every once in a while I would go to Curve Editor, select and delete all keys leaving only:
CC_Base_R_ToeBase \Rotation X
CC_Base_L_ToeBase \Rotation X
This is how my timeline looked at the end from Curve Editor perspective (only 2 curves):
At the end when all is done and you are happy with the result, go ahead and bake with Flatten All Motion with Constraint option. Delete reach dummies once motion is baked.
It might seem overly complicated, but it's actually not. Once you get done a few poses, you'd come up with steady routine and your own shortcuts for animating Reach dummies and Toe bones at the timeline.
It's also a good practice to keep your skills for manual animations sharp.