What Is Animation Retargeting?
What you'll learn: This guide covers animation retargeting in Unreal Engine 5 using the IK Retargeter, animation retargeting in Unity through the Humanoid avatar system, mocap retargeting in Blender, common IK Retargeter UE5 configuration problems, and how to choose animation assets designed for clean retargeting.
Animation retargeting is the process of applying animation data from one character skeleton to a different character skeleton. When you download a motion capture animation pack or import a Mixamo FBX, the animation was captured on a performer and applied to a reference skeleton. Your game character almost certainly has a different bone hierarchy, different limb proportions, and different bone naming conventions. Animation retargeting bridges that gap.
Understanding the underlying animation system is key to successful retargeting between different character rigs.
Without retargeting, imported animations cause characters to warp into impossible poses, float off the ground, or collapse entirely. With proper retargeting, a locomotion set captured for a standard humanoid skeleton transfers cleanly to a stylized game character, a creature rig, or a non-standard skeleton — preserving the natural motion quality while adapting the movement to the target character's proportions.
Understanding retargeting is essential for any game developer or technical animator who works with mocap assets, animation libraries, or cross-engine animation pipelines.
Why Animation Retargeting Is Necessary
Motion capture data encodes bone rotations relative to a specific skeleton. That skeleton has specific bone names (which engines use to identify anatomy), specific bone orientations (the rest pose), and specific limb proportions (the performer's actual body measurements).
When you apply animation data from skeleton A to skeleton B, three things can go wrong. Bone name mismatches cause the engine to ignore that joint. Rest pose differences between an A-pose and T-pose make rotations compound incorrectly, pointing limbs in wrong directions. Proportion differences — a performer with 90cm arms driving a character with 70cm arms — result in the character's hands clipping through their body during reach animations. Retargeting solves all three problems by mapping joints between skeletons, normalizing rest poses, and applying proportion correction to translation-based movement.
Animation Retargeting in Unreal Engine 5
UE5 has the most powerful built-in retargeting toolset available in any game engine. The primary tool is the IK Retargeter, which provides visual, interactive control over the retarget mapping.
Setting Up the IK Retargeter
Prerequisites: You need two IK Rigs — one for the source skeleton and one for the target skeleton. An IK Rig defines the retarget chains for the skeleton (spine chain, left arm chain, right leg chain, etc.).
Step 1: Create IK Rigs. In your Content Browser, right-click → Animation → IK Rig. Assign the Source Skeleton asset. In the IK Rig editor, define retarget chains: a Root chain (single bone), Spine chain (pelvis to chest), Left/Right Arm chains, Left/Right Leg chains, Head chain, and hand/foot detail chains. Repeat for the Target Skeleton.
Step 2: Create the IK Retargeter. Right-click → Animation → IK Retargeter. Assign the Source IK Rig and Target IK Rig. The retargeter will attempt to auto-map chains by name.
Step 3: Preview and Adjust. Open the IK Retargeter. In the viewport, you'll see both characters side by side — source playing animation, target receiving the retargeted result. Fix root position if the target character floats or sinks. Enable Stride Warping to correct foot placement for proportion differences. Fix spine twist by manually adjusting chain mapping for characters with different spine bone counts.
Step 4: Batch Retarget. Once the retargeter looks correct on a test animation, use Asset → Export Animations to batch-retarget an entire folder of Animation Sequences to the new skeleton in one operation.
Retargeting Mixamo to Mannequin in UE5
Mixamo uses a different skeleton and rest pose than UE5's Mannequin. Import the Mixamo FBX into UE5 to create a new skeleton asset. Create an IK Rig for the Mixamo skeleton — Epic has shared community presets for this. Create or use the existing IK Rig for the Mannequin skeleton. Create a Mixamo → Mannequin IK Retargeter. Batch export all Mixamo clips to Mannequin Animation Sequences. Community retargeting presets for this path are widely available on the UE Marketplace and in the Unreal Engine forums.
Retargeting MoCap Online Assets in UE5
MoCap Online's animation packs use a skeleton designed for minimal friction against the UE5 Mannequin hierarchy. Bone names and orientations follow UE conventions, which reduces or eliminates the manual chain-mapping step. For most packs, the retarget works with the default auto-mapping — adjust only if you see visible problems in the preview.
Animation Retargeting in Unity
Unity's Humanoid avatar system handles retargeting differently from UE5 — it uses a standardized internal skeleton as an intermediary.
How Unity's Avatar System Works
When you import a FBX with Animation Type set to Humanoid, Unity reads the FBX skeleton bone names and auto-maps them to Unity's 55-bone Humanoid definition. It creates an Avatar asset recording this mapping. At runtime, all Humanoid animations are expressed in terms of the internal skeleton, which means any Humanoid animation can play on any Humanoid character without explicit retargeting. Stylized characters with non-human proportions get proportion-corrected by the avatar system, which can reduce animation quality on characters far from standard human proportions.
Setting Up Humanoid Import
Select the FBX in the Project panel → Inspector → Rig tab. Set Animation Type to Humanoid. For Avatar Definition, choose Create From This Model (first time) or Copy From Other Avatar (for subsequent characters using the same rig). Click Configure... to open the Avatar editor — green bones are correctly mapped, red bones indicate missing or mismatched assignments. Fix any red bones by dragging them to the correct slot in the Mapping view. Click Done and Apply.
Generic Rig Retargeting in Unity
For non-humanoid characters (creatures, vehicles, stylized humanoids that don't map well to Humanoid), Unity uses Generic rigs — direct FBX bone animations with no avatar intermediary. Generic animations are skeleton-specific and don't retarget between different skeletons. For cross-skeleton retargeting with Generic rigs, third-party tools like the Animation Rigging package or UniRetarget are needed.
Animation Retargeting in Blender
Blender doesn't have a built-in retargeting system as polished as UE5's IK Retargeter. The two main approaches are Auto-Rig Pro and BVH retargeting.
Auto-Rig Pro (Recommended)
Auto-Rig Pro is a third-party Blender addon that includes a retargeting module. Import the source armature and animation. Have your target armature open in the same scene. Open Auto-Rig Pro → Remap tab. Select source and target armatures, define which bones correspond using the bone mapping UI, and apply the retarget — it bakes the remapped animation onto the target skeleton.
BVH Retargeting Workflow
For BVH files (common in mocap archives), Blender handles the import natively. After import, the BVH creates an armature with the captured motion baked in. Retargeting from this to a Rigify or Metarig armature requires Auto-Rig Pro or manual constraint-based retargeting using Copy Rotation constraints on each bone.
Common Retargeting Problems and Fixes
Hands and fingers don't move: Most standard retargeters handle body chains but skip fingers. Add explicit finger bone chains to your IK Rigs (UE5) or manually map finger bones in the avatar (Unity).
Character leans forward or backward: Rest pose mismatch between A-pose and T-pose skeletons. In UE5, use the Source/Target Post Retarget Pose settings to align rest poses before retargeting.
Foot sliding after retarget: Normal for proportion-different characters. Enable Stride Warping in UE5's IK Retargeter to apply automatic foot planting correction based on the target character's leg length.
Root motion doesn't translate: The Root chain must be explicitly mapped in UE5's IK Retargeter. In Unity, the Apply Root Motion checkbox on the Animator component controls whether root motion is used or discarded.
Spine looks stiff: Source animation has more spine bones than the target. In UE5, map multiple source spine bones to fewer target spine bones using the chain distribution settings — this blends spine rotation across available target bones.
Retargeting Performance: Tips for Production Scale
Batch retarget early: Set up your retarget chains and presets when the first animation arrives, not when you have 200. Batch retargeting 200 animations takes the same setup time as retargeting 1.
Build a retarget library: Save retargeter assets and IK Rig assets organized by skeleton family. A studio working with multiple character types should have retargeters for each source→target pair, ready to apply to new animation deliveries.
Test with edge-case animations first: Your retarget setup's weaknesses show fastest on animations with extreme extension (full reach, high kick, prone). If those look correct, the standard clips will be fine.
Use reference characters for preview: Always preview retargeted animations on the actual game character mesh, not just the skeleton. Mesh deformation reveals issues — especially hand/foot penetration and spine compression — that skeleton preview misses.
IK Retargeter UE5: Advanced Configuration for Mocap Retargeting
The IK Retargeter UE5 is the most capable free retargeting tool available for game developers. Getting good results from mocap retargeting requires understanding how to configure chains, reference poses, and stride warping for your specific character proportions.
Chain configuration for mocap data. A basic humanoid IK Retargeter UE5 setup needs chains for: Root (single bone), Spine (pelvis to chest or neck), Head (neck to head), Left and Right Arm (shoulder to hand), and Left and Right Leg (hip to foot). Skipping the Root chain causes the character to stay at world origin while the animation plays. Each chain's Start and End bone must be set explicitly in the IK Rig editor — auto-detection doesn't always find correct boundaries for non-standard skeletons.
Reference pose alignment for mocap retargeting. Mocap retargeting accuracy depends on aligning the source and target skeletons in the same reference pose. If your mocap pack skeleton uses an A-pose and your target uses a T-pose, rotations will compound incorrectly on the target. In the IK Retargeter UE5, set both the Source and Target Retarget Pose to match. This step is responsible for the majority of visibly broken retargets when skipped.
Stride warping for proportion-different characters. When the target character has significantly different leg lengths from the source performer, foot sliding is the most common result. Enable stride warping in the Global Settings panel of the IK Retargeter UE5. Set Warp Scale to 1.0 as a starting point and preview with a locomotion animation. Adjust Warp Scale up for longer-legged targets, or down for shorter-legged targets, until the stride looks natural at the target character's scale.
Batch retarget animation unreal engine production workflow. Once the IK Retargeter UE5 is configured and the preview looks correct, use Asset → Export Animations to retarget the entire mocap pack at once. Select the source folder of Animation Sequences and the target output folder. The retargeter processes each animation and creates new Animation Sequences on the target skeleton. For a 60-animation mocap pack this typically takes 2–5 minutes.
FAQ: Animation Retargeting
Do I need to retarget if I use MoCap Online animation packs?
MoCap Online packs are formatted to minimize retargeting work against UE5 Mannequin and Unity Humanoid rigs. For Unreal Engine, the IK Retargeter auto-mapping handles the transfer with minimal manual chain adjustment. For Unity, setting Animation Type to Humanoid handles it automatically. Custom rigs still require the standard retargeting workflow.
Can I retarget creature animations to a humanoid character?
Not directly — the bone topology is too different. Creature-to-humanoid retargeting requires a custom rig mapping creature limbs to humanoid equivalents, which is a manual rigging task rather than a standard retargeting workflow.
What's the best free retargeting tool?
UE5's IK Retargeter is the most capable free tool available. Unity's Humanoid avatar system handles humanoid-to-humanoid animation retargeting for free within the engine. For Blender, Auto-Rig Pro ($40) is the practical production choice over the free Rigify retargeting support.
How long does animation retargeting take per animation?
For a well-configured retargeter with matching skeletons: under 1 minute per animation (batch). For a new skeleton pair requiring chain setup: 2–4 hours to configure the IK Retargeter, then batch time after. This is why a production-ready animation library already aligned to your skeleton saves significant pipeline time.
How do I retarget animation in Unreal Engine 5 from a mocap pack to my character?
To retarget animation in Unreal Engine 5, create an IK Rig for the mocap pack's source skeleton and an IK Rig for your target character. Create an IK Retargeter that maps between them and let it auto-map chains by name. Preview the result, fix any issues using stride warping and root retarget settings, then use Asset → Export Animations to batch-retarget the entire pack to your target skeleton.
How does animation retargeting in Unity work for mocap assets?
Animation retargeting in Unity for mocap assets works through the Humanoid avatar system. Set Animation Type to Humanoid on the imported FBX. Unity auto-maps the bones to its 55-bone Humanoid definition and creates an Avatar. Any Humanoid animation then plays on any Humanoid character without additional steps — the avatar system handles proportion correction at runtime. Non-standard skeletons need Generic rig workflows instead.
What is mocap retargeting and why is it more challenging than standard retargeting?
Mocap retargeting transfers motion capture animation — recorded from performer body tracking — to a target character rig. It is more challenging than retargeting hand-keyed animation because mocap data encodes highly specific biomechanical details: exact foot contact timing, pelvis counterrotation, and subtle limb relationships that break down when proportions are mismatched. Mocap retargeting across significantly different proportions requires additional tools — stride warping for foot contact, spine chain distribution for different vertebra counts, and sometimes manual curve editing.
What does the IK Retargeter UE5 provide that direct bone mapping can't?
The IK Retargeter UE5 uses inverse kinematics to preserve end-effector positions (where hands and feet land) even when limb lengths differ. It provides stride warping for automatic foot contact correction. It retargets chains rather than individual bones, handling differences in spine bone count. And it supports batch export of entire animation folders to a new skeleton in one operation — making it practical for production-scale mocap retargeting of large animation libraries.
Get Animations That Retarget Cleanly
The fastest path to production-ready character animation starts with assets designed for retargeting. MoCap Online's animation packs are built from the ground up for game engine workflows — using skeleton hierarchies aligned with UE5 Mannequin and Unity Humanoid conventions.
Browse the motion capture animation library to find packs for your character class, then download the free animation pack to test the retarget workflow in your specific engine before purchasing. For workflow guides and engine-specific tutorials, visit the MoCap Online animation blog.