Correcting Motion Capture is only part of the motion editing process. The real skill is taking that motion and turning into the thoughts, feelings and emotions of a character.
Just like any animator you need bring your character to life by showing the audience what your character is thinking and feeling by the way it moves. Yes, the motion needs to be accurate, have squash and stretch, weight, anticipation, appeal, etc. But if it doesn’t have a reason behind it, an emotion or objective, then it just becomes nice motion on a moving object.
If you’ve never edited motion capture before this can feel like a pretty daunting task. You’re usually looking at a character with hundreds of key frames, on every object and every frame. Then there are errors to fix, changes to make, technical and artistic challenges to meet. And all this usually needs to “look cool” and be finished by tomorrow, if not sooner!
This is usually when panic starts to sets in. You begin to wonder if all the bad things you’ve heard about motion capture are true. Suddenly you’re up to your neck in FCurves and Animation Layers, deleting key frames and animating into the small hours, hating the idea of ever using mocap again.But, I want to show you how to avoid all this.
Using my workflow as an example I‘m going to show you how to break the editing process in to 4 stages. Then, break each stage down, step by step, so you know what to do and when to do it.
My hope is this will give you the techniques you need to build your own workflow or maybe give you a few ideas to add to your existing one.
Table of Contents
Before You Start
It may sound obvious now, but before you start working on any file, make sure it’s the right one. When you’re processing hundreds of files with different performers, characters, props, takes and frame ranges, it’s easy for mistakes to happen.
Compare the file you are about to edit to the video reference from the mocap shoot. Make sure the character in your scene moves in exactly the same way as the performer in the video. If it doesn’t, you need find out why, before you go any further. There’s nothing worse than working on a file all day only to find out it’s the wrong one.
1. Understand the How, Why, Where of the Action
The secret to good motion editing is understanding exactly what the character is doing, why they are doing it and then communicating that idea as clearly as possible to an audience.
Begin by discussing the action with your lead, supervisor, designer, programmer or anyone involved with the character. Ask them how the action should be performed, why the character is doing it, and where it’s taking place. If you’re working on your own, use the same frame-work to try to describe the action. Avoid simple phrases like “stand still point gun“. Instead think about the how, why and where of the action. For example, “crashing into cover behind a post, the hero stands alert, ready to return fire”.
The first thing to understand are the mechanics of the action (the how), especially if you’re transferring human motion on to a non-human character. Play the mocap back on a loop and view it from every possible angle. If you can, try performing the action yourself so you can feel what’s happening. Study how the character moves:
- Speed changes (slow-in and slow-outs),
- Overlapping actions (follow-through),
- Compression and extension (squash and stretch),
Then think about why the character is moving:
- What is the character’s motivation?
- What is the thought process, idea or objective behind the action?
- What is the character’s physical and mental state?
- What have they just done?
- What are they about to do?
Finally look at where the action is happening and what the technical requirements are:
- Does the action need to happen in a precise location?
- Interact with an object?
- Start or end in a specific pose?
- Face a particular direction?
- Cover a certain distance?
- Match an exact timing?
Make sure you know the answers to these kinds of questions before you begin. The worst mistake you can make is to open a file, have a quick look at it, assume you know what’s happening and start editing. If you don’t know what your character is supposed to be doing, it’ll be impossible to show it to an audience.
2. Plan Your Edits
Now you know what your character is supposed to be doing, you can plan how to edit the file to make that idea as clear as possible.
The amount of time you spend planning should reflect how and where the actions will be used. For example, a complex action for a hero character will need more planning than a simple action for a background character.
Start by checking the action can meet all the necessary technical requirements. While it’s not always possible to perform every action perfectly, all the elements should be there for you to adjust. For example, distances can be modified, alignments refined, poses corrected, timings adjusted, actions blended. But if any of these elements are missing, you’ll need to decide if it’s going to be easier to create them yourself or reshoot the action.
When you’re sure the action contains everything it does need, you need to make a note of everything it doesn’t. Besides additional variations or unsuccessful attempts, motion captured files often contain data that isn’t needed to create the final animation. For example, as the performer gets into position or waits for “Action” and “Cut” to be called. Also parts of the animation may need reducing or speeding up to make the action feel more responsive. For example, too many steps as the character stops or a long “wind-up” anticipation before a punch.
Once you’ve checked the overall animation, the remaining fixes usually fall into 3 main categories – which also happens to be the perfect order to do them in:
- Data clean-up and re-targeting,
- Technical changes,
- Artistic enhancements.
Start by looking for errors that might have been created during the data clean-up and re-targeting stage:
- Incorrect actor performance
- Noisy (shaky) character motion,
- Flipped joints,
- Unnatural limb positions,
- Strange movements,
Then make a list of any technical issues that need fixing:
- Character’s alignment,
- Motion paths and trajectories,
- Foot floor contacts,
- Mesh intersections,
- Object interactions,
- Loops and Poses.
Finally, make a list of the artistic changes needed to enhance the performance:
- Exaggerating poses,
- Refining motion,
- Adjusting weight and balance
- Modifying timings,
- Adding missing detail.
It may feel like you’re wasting time planning rather than editing, especially if you have a short deadline. But planning everything before you start can save you time and problems later – plus it’s much easier to do before you’re up to your neck in Key Frames, Animation Layers and Constraints.
3. Correct Technical Problems
Before you can enhance the way your character moves, you need to make sure the foundation of that movements is correct.
Start by fixing any errors that were created during the tracking or remapping process. For example, a hand that flips or a head looking in slightly the wrong direction. It’s usually better to do this by reprocessing the original mocap data rather than editing the processed character animation. Reprocessing the file will help restore any lost data and can also reveal problems that might affect other files.
The last thing to do before you begin editing is to remove any unnecessary frames from the animation. For example, the frames before and after the section you’re going to loop or the stationary frames before and after the character moves. Removing these frames now will help you avoid wasting time fixing a problem no one will ever see.
Once the remapping errors have been fixed and unwanted frames removed, you’re ready to start editing the character motion. Go back to your list of edits from the previous step and work through them one a time. Start with the largest adjustments that affect the entire character. For example, the characters position in the scene or it’s pose at the start and end of the animation. Then correct each of the character’s limbs, starting at the root of the hierarchy as this normally drives the action. For example,
- Shoulder->Upper Arm->Forearm->Hand->Fingers
- Hips->Upper Leg->Lower Leg->Ankle->Toes.
Or if you are editing an object using IK, begin at the top of the chain and then work your way back up from the end effector. For example:
Make sure each limb has a smooth path of action otherwise your animation can feel “clunky” and unnatural. Study the shape of the FCurves in the FCurves window or turn on Trajectories in the Viewer window. For example, during a walk look for the wave motion of the hips as they rise and fall, the arcs of the arms as they swing, the figure of 8 movement created by the wrists or the straight line of the foot on the floor.
When editing key frames, try to keep as much of the original mocap data as possible. Adjust the position of an object with an Animation Layer or by moving or scaling FCurves. Try to avoid changing a single key frame and then deleting the surrounding ones. Only delete key frames when necessary and then only do it one frame at a time. The more key frames you delete, the more detail you remove. The more detail you remove, the more animating you will need to do to replace it. The more animating you need to do, the more time and money the mocap will ultimately cost.
Before you make each edit, take a moment to think about what you’re going to do and how you’re going to do it. There are situations where a single offset can correct several issues and others where it will break more things than it fixes. Working this way will help you learn to recognise the most common problems with mocap and the best ways to fix them.
Most importantly of all, SAVE YOUR WORK AFTER EACH FIX. This will give you a point to return to if the next edit breaks something, or if your machine crashes or the file gets corrupted. DO NOT save over the same file again and again. Save a new version of the file by adding “_V001, _V002, _V003” etc. to the end of the file name. MotionBuilder only creates a limited number back-up files file, so it’s better to save your own you can return to if something breaks.
4. Create a Character Performance
Once all the technical problems have been fixed, it’s time to move on to the artistic side of the process: creating a believable character performance.
Begin by reviewing the animation. Analyse the character’s movements and gestures and ask yourself if they clearly show what your character is thinking and doing. If they don’t, you need to plan what changes you can make to correct this.
It’s crucial you know exactly what you want the final animation to look and how you’re going to achieve it BEFORE you start editing. If you don’t, things can get very messy, very quickly. You’ll find yourself constantly editing the same sections of the animation as you search for something that looks right. Because of this, the work will take longer than it should. And eventually the idea behind the action will be lost and the final animation will look confused and lifeless.
Break the motion down into its key moments: the anticipation, the action and the reaction. Then make your edits during these moments. For example, reposition a foot during a step or realign a grab as the character reaches for the object. Some edits will require adjusting all three sections of the motion to maintain believability. For example, editing the height of a jump will also need changes to the anticipation take-off and landing reaction to keep the sense of weight and force. Increasing the speed of a punch action will give it greater impact but you will also need to change the anticipation and reaction to make it convincing.
Maintaining the believability of the actions is also crucial when you’re editing. Your edits need to find the right balance between over exaggeration and realistic believability. The existing motion already has a grounding in reality based on how a person moves in this universe. Your job is to translate that motion into the actions of a character living in the fictional world of your project.
Once you’ve decided what edits you’re going to make, try to make them on the extreme frames of those key moments. The same “extreme” frames you would create if you were hand animating the action. For example, just before or after a limb moves or as it pauses to change direction. This will help maintain the illusion your characters movements are driven by a thought process not a key frame on a time line.
Use Animation Layers or move and scale FCurves to modify the animation on an object. Only delete key frames when absolutely necessary and then only do it one frame at a time. Remember, every time you delete a key frame you are removing detail from the animation.
Alternatively, if the edit you are trying to make requires a lot of key frames, the change might be too big. At this point you need to decide if it will be easier to continue editing, re-shoot the action or hand animate it.
Finally, try to avoid the temptation to adjust everything just because you can. Remember, you’re trying to show what the character is thinking and doing, NOT how good you are at making something move. Even if the motion looks amazing, if it doesn’t have a thought, feeling or emotion behind it, the audience will never really care about your character.
Remember, your job is to show the audience what your character is thinking and feeling, not how well you can make something move.
You need to translate the performance of an actor in a mocap volume into the thoughts and actions of your character.
Yes, the animation needs to be good, have squash and stretch, anticipation, overlap, appeal, etc. But if there isn’t a reason behind the movement, an emotion or objective, then it is just nice motion on a moving object.
Do you have any tips from your own workflow? Feel free to share them in comments below.