Create pose from existing armature

Question

I have two armatures with all of the same bones. Armature A is a basic character T-stance, Armature B is of a run animation. I had first attempted to copy the pose from Armature B to Armature A, but realized that there was no pose, and that the positions of the bones of Armature B where baked into (I think that's the proper term) the armature, meaning there was no pose to copy.

Rest Poses: T-pose Armature A on left, Armature B's (the one with animation) on right

Is there a way to create a pose of Armature A using the positions of the bones of Armature B?

An example blend can be found here:

Bip001 is the primary armature that the model is bound to, Bip001.001 is the armature with the animation I am attempting to apply to Bip001. (Bip001 == Armature A, Bip001.001 == Armature B from the above explanation).

Answer 1

Here is a script I've been working on to do this for bvh files. Basically it adds a copy transform constraint to each pose bone, then using Object.convert_space, retargets animation to another rig with same bones.

It's good practice to keep scale on armatures to unity, to avoid issues. Applying scale to both armatures. Ctrl-A scale will make the scale (1, 1, 1). I applied rotation as well and put the armature objects at location (0, 0, 0) before running script..

import bpy
from bpy import context

remove_constraints = False
scene = context.scene
rig1 = scene.objects["hands_reference_skeleton"]

rig2 = scene.objects["hands_reference_skeleton.001"]
if not rig2.animation_data:
    rig2.animation_data_create()
rig2.animation_data.action = None

# add copy transform constraint to each bone
for pb in rig2.pose.bones:
    ct = pb.constraints.get(pb.name)    
    if ct is not None:
        ct.influence = 1
        continue
    ct = pb.constraints.new('COPY_TRANSFORMS')
    ct.name = pb.name
    ct.target = rig1
    ct.subtarget = pb.name

action = rig1.animation_data.action

f = action.frame_range.x
# add a keyframe to each frame of new rig
while f < action.frame_range.y:
    scene.frame_set(int(f))
    context.view_layer.update()
    r2 = rig2.evaluated_get(context.evaluated_depsgraph_get())
    for pb in r2.pose.bones:
        #pb2 = rig1.pose.bones.get(pb.name)
        m = rig2.convert_space(
            pose_bone=pb, 
            matrix=pb.matrix,
            from_space='POSE', 
            to_space='LOCAL',
            )
        if pb.rotation_mode == 'QUATERNION':
            pb.rotation_quaternion = m.to_quaternion()
            pb.keyframe_insert("rotation_quaternion", frame=f)
        else:

        # add rot mode checking 
            pb.rotation_euler = m.to_euler(pb.rotation_mode)
            pb.keyframe_insert("rotation_euler", frame=f)
        pb.location = m.to_translation()

        pb.keyframe_insert("location", frame=f)
    f += 1

# set constraints to zero or remove entirely.
for pb in rig2.pose.bones:
    ct = pb.constraints.get(pb.name)    
    if ct is not None:
        if remove_constraints:
            pb.constraints.remove(ct)
        else:
            ct.influence = 0