What Animation Retargeting Is
Animation retargeting is the process of transferring animation data from one skeleton to another. It is one of the most important technical concepts in game animation production because the skeleton an animation was built for almost never exactly matches the skeleton your character uses. The animation system in your engine applies the animation to the target model by mapping bones between skeletons — understanding when retargeting is required, how to do it correctly, and how to avoid it entirely saves significant production time.
Why Retargeting Is Needed
Every animation clip is bound to a specific skeleton — a hierarchy of named bones with specific proportions. The animation system applies the animation data to whatever target model you assign, matching bones by name. If bone names match, the animation plays. If they do not, you see a T-pose.
Skeletons differ in bone names, bone count, hierarchy structure, proportions, and rest pose. Retargeting maps the animation from one skeleton to the other by transferring rotations relative to a rest pose, so that proportion differences between skeletons are absorbed. A performer with long arms and a character with short arms will both raise their hand to the same relative height despite the absolute bone length difference. This space-relative approach is how all major engine retargeting systems work.
How to Avoid Retargeting Entirely
- UE5 — buy packs built for the UE5 Mannequin skeleton. UE5 Mannequin-targeted packs import with zero retargeting for standard projects.
- Unity — configure both character and animation as Humanoid. Unity's avatar system applies the animation automatically through its internal humanoid mapping.
- Blender — use MoCap Online Blender-specific FBX exports with correct axis and scale for Blender 4.x.
Retargeting in UE5
UE5 uses the IK Retargeter as its primary retargeting animation system. The workflow:
- Create an IK Rig for the source skeleton — define IK chains for spine, arms, and legs.
- Create a second IK Rig for the target model skeleton.
- Build an IK Retargeter that maps chains between the two IK Rigs.
- Align the retarget pose to a matching T-pose or A-pose. Pose mismatch is the primary source of retargeting artifacts.
- Preview and adjust chain mappings until artifacts disappear — the Retargeter preview shows results in real time.
- Right-click any animation asset in Content Browser → Retarget Animation Assets to batch-process your entire library.
For MetaHuman, UE5 ships a pre-built retargeter (RTG_UE5Mannequin_To_MetaHuman) that applies the animation directly without manual chain setup.
Retargeting in Unity
Unity's Humanoid avatar configuration is a retargeting animation system embedded in the import pipeline. Set Animation Type to Humanoid on both source and target FBX assets, configure the Avatar Definition for each, and Unity handles bone mapping automatically. The Muscle definition in the Avatar constrains retargeted rotations to anatomically plausible ranges, which eliminates most breakage from proportion mismatches. Generic rig characters must use animations built for their exact skeleton — the automatic Humanoid mapping does not apply.
Retargeting in Blender
Blender uses a constraint workflow rather than a built-in one-click retargeter. Add Copy Rotation constraints on each bone in your target rig targeting the corresponding bone in the source (mocap) rig. Add Copy Location on the root to transfer world movement. Bake the result (Pose → Animation → Bake Action) with Visual Keying and Clean Curves enabled to create a new Action on your target rig independent of the constraint system. Remove all constraints after baking. For Rigify rigs, target the deformation bones (DEF- prefix) rather than the control bones (CTRL- prefix) for clean results.
Where Proportion Mismatches Cause Problems
Retargeting works cleanly when source and target skeletons share similar proportions and joint axis orientations. Problems arise at extremities — hands, fingers, feet — where small proportion differences produce large visual errors because the joint chains are short and the lever arm amplifies any offset. Characters with non-human proportions — very long necks, oversized heads, digitigrade legs — require manual correction at the problem joint chains regardless of which retargeting system you use.
Common Retargeting Problems
- T-pose after import — skeleton mismatch. Assign the correct skeleton at import or run the retargeter.
- Limbs rotating wrong — rest pose mismatch. Align the retarget pose first before running retargeting.
- Root motion not transferring — include the root bone in IK Rig chains.
- Broken wrists or fingers — proportion mismatch at extremities. Adjust chain FK blending weights in the IK Retargeter, or manually correct affected joint chains.
The Best Retargeting Workflow
The best retargeting workflow is the one you never have to run. MoCap Online packs ship in engine-native formats for Unreal Engine, Unity, and Blender to eliminate retargeting entirely for standard characters. Download a free sample pack to verify compatibility with your skeleton before purchasing a full collection. See the animation blend tree guide for next steps after getting animations onto your character.