Retargeting is the process of transferring animation from a source skeleton to a different target skeleton. A successful preview is only the beginning. Production-quality retargeting must preserve the performance while managing different proportions, reference poses, chain definitions, root behavior, and contact points.
Unreal Engine 5 uses IK Rig and IK Retargeter assets for this workflow. The exact editor layout can evolve between releases, but the underlying process remains consistent: prepare both rigs, define equivalent chains, align poses, configure root and chain behavior, preview representative motions, and export new target animations.
Start with a clean source import
Import the mocap animation against the skeleton it was authored for. Do not force an animation-only FBX onto a different target skeleton merely because Unreal Engine accepts the selection. A clean source asset gives the retargeter reliable bone transforms and preserves a reference that can be reused for multiple characters.
Before retargeting, verify:
- The source sequence plays correctly on the source mesh.
- The frame range and sample rate are correct.
- Root Motion or In-Place behavior is understood.
- The source hierarchy contains the expected pelvis, limbs, spine, neck, and root.
- There are no scale spikes or broken transforms.
The import checks are covered in How to Import FBX Animations into Unreal Engine 5.
Step 1: create an IK Rig for each skeleton
Create one IK Rig for the source skeleton and one for the target skeleton. Assign a representative preview mesh to each asset. The preview mesh matters because you need to inspect proportions and pose alignment while configuring the retarget.
Set the retarget root, commonly the pelvis or a project-specific equivalent. The retarget root helps the system reason about overall body motion and proportional differences. It is not always the same as the top-level root bone that stores world displacement.
Step 2: define equivalent retarget chains
Create chains for corresponding body regions. Typical chains include:
- Left and right legs.
- Left and right arms.
- Spine.
- Neck and head.
- Optional fingers, clavicles, toes, or twist structures when the target needs them.
Chain names do not need to match individual bone names, but the source and target rigs must expose equivalent semantic chains. Keep the definitions intentional. Including too many auxiliary or twist bones inside a primary chain can produce unstable results; excluding important deformation or contact bones can reduce fidelity.
Step 3: create the IK Retargeter
Create an IK Retargeter that uses the source IK Rig and assign the target IK Rig. Confirm that source chains map to the correct target chains. Automatic mapping can save time, but every important chain should be reviewed.
Preview a neutral idle first. If the character is already distorted before motion begins, fix the chain or pose setup before tuning dynamic clips.
Step 4: align the retarget poses
Reference-pose mismatch is one of the most common causes of poor retargeting. A source in an A-pose and a target in a T-pose can create raised shoulders, bent elbows, twisted wrists, or incorrect arm spacing even when the chain mapping is correct.
Edit the retarget pose so equivalent body parts point in compatible directions. Focus on:
- Pelvis orientation and body height.
- Spine and chest posture.
- Clavicle, shoulder, and upper-arm angle.
- Elbow bend and wrist orientation.
- Knee direction, foot angle, and stance width.
- Head orientation.
A retarget pose is not an attempt to reshape the target into the source character. It is a rotational alignment that gives equivalent chains a compatible starting relationship.
Step 5: configure pelvis and root motion
Characters with different leg length and torso proportions need deliberate pelvis behavior. If the pelvis follows source translation without proportional adjustment, the target can float, sink, overextend the legs, or compress the stance.
Test vertical and horizontal pelvis motion separately. Review standing idles, crouches, ground interactions, steps, and actions with strong weight shifts. A setting that looks acceptable on a walk can fail on a kneel or sit.
For Root Motion sequences, verify that the target output preserves the intended displacement and rotation. Source root, target root, and pelvis handling must agree. For In-Place output, confirm that unwanted displacement is not introduced by the retarget.
Step 6: use IK goals for contacts that matter
Forward-kinematic chain transfer preserves much of the pose, but proportion differences can move hands and feet away from their original world-space contacts. IK goals can help maintain important end-effector positions.
Prioritize IK for actions with visible constraints:
- Feet planted during an idle, turn, or interaction.
- Hands holding a weapon or prop.
- A hand touching a table, wall, wound, or another character.
- Knees or elbows contacting the ground.
IK is not a substitute for compatible proportions or a good retarget pose. Excessive pinning can distort the limb or transfer the problem into the hips and shoulders. Use it where contact matters, then inspect the whole body.
Step 7: test representative extremes
Do not validate a retargeter using only one neutral animation. Build a compact test set that exposes different failure modes:
- Neutral standing idle.
- Walk or run with visible foot plants.
- Deep crouch or kneel.
- Arms overhead and arms crossing the torso.
- Strong pelvis translation.
- Turn with rotation.
- Prop or two-hand contact.
Fix the general retarget setup with this set before exporting hundreds of sequences. Asset-specific exceptions can be handled later without destabilizing every other animation.
Step 8: export target animations
Once the preview is reliable, export duplicated Animation Sequences for the target skeleton. Keep the generated files in a separate target folder and preserve consistent naming. This makes it clear which assets are original source data and which are editable retargeted output.
After export, test the actual Animation Sequence, Animation Blueprint, montage, and gameplay character. Runtime blending, compression, notifies, collision, and controller movement can reveal issues that the retarget preview does not show.
Common retargeting problems
Feet slide or float
Check pelvis scaling, root behavior, target proportions, chain definitions, and whether IK goals are active where expected. Also verify movement speed for In-Place locomotion. Retargeting is not always the sole cause.
Arms look too high or too low
Review the retarget pose, especially clavicle and upper-arm rotations. A-pose and T-pose mismatch commonly produces this result.
Hands miss a prop
Different arm length changes reach. Use an appropriate IK goal or adjust the target prop/socket setup. Two-character and prop interactions usually require target-specific correction.
The target sinks during crouches
Inspect pelvis translation and proportional scaling across low poses. A setting tuned only for standing motion may overcorrect deep compression.
Root Motion distance changes
Check source and target root configuration and the retarget operation stack. Confirm that the exported target sequence contains the expected root track before changing gameplay code.
Production checklist
- Correct source animation and source skeleton.
- Source and target IK Rigs with deliberate retarget roots.
- Equivalent, reviewed chain definitions.
- Aligned retarget poses.
- Pelvis and root behavior tested on high and low poses.
- IK goals used only where contacts need them.
- Representative extremes tested before batch export.
- Target sequences exported to a separate folder.
- Gameplay, montage, and blending tested after export.
Retargeting quality begins with suitable source motion. Browse game-ready mocap animation packs and review the skeleton and technical information on each product page before choosing a source library.