Using (Free) Mocap Data for Game Character Animation in Unity

I mentioned in my last blog post that I’d experimented with using motion capture data as a way to quickly animate characters for a game jam in Unity. Seeing as I’m neither an artist or an animator, the thought of simply being able to apply a data file of “walking”, “jumping”, “shooting” etc. and watch the character do those actions in a life-like way is very appealing, compared to laboriously editing sprite sheets or tweaking animation keyframes.

Friends who know more about animation than me point out that motion capture is a tool designed to help animators, rather than a tool designed  to replace animators, but for my prototypes I’d be quite happy to use fairly raw motion-captured animations – they’d certainly be better than anything I could draw.

I encountered a fair number of issues along the way, so here’s a summary of my what I learned:

 

Step One : Acquire some Mocap Data

If you want high-quality ready-to-use character animations for Unity, then Mixamo seems the de facto place to go. However, they’re not cheap, so I sought out some free alternatives:

• The Carnegie-Mellon Graphics Lab Motion Capture Database has a large range of motions which can be copied, modified, or redistributed without permission. The original raw data is captured as ASF/AMC format, which I have no idea how to use. Fortunately, there are several repackaged versions, such as this version in more common BioVision Hierarchy (BVH) format.
• Japanese site mocapdata.com, which claims to be “the world [sic] biggest state of the art motion capture library on the earth” has several hundred free animations in various categories licenced under a CC Attribution licence, together with some ludicrously expensive “premium” animations… (such as this animation pack, which costs $82,200!!!). Animations are often recorded by different actors, and in various file formats (FBX, BIP, C3D, BVH). Rather annoyingly, though, the rigs used in the FBX downloads don’t appear to be compatible with Unity’s MecAnim system, so I had to download either the BIP or BVH format and convert them instead (details below).
• http://hyperlearn.p.ht/category/adobe-flash/ has ~400 everyday/sports animations in BIP format. Must be downloaded individually through an annoyingly ad-laden site, and despite being described as “free”, it’s unclear what the licence for use of these files is.
• http://gfx-motion-capture.blogspot.co.uk/ has around 50 free mocap animations in either BIP, BVH, or FBX format.
• The Ohio State University computing centre motion capture lab has a range of common male and female motions in various formats.

 

Step Two : Cleanup and Convert to FBX

Mocap data can be stored using a number of different file formats – FBX, BVH, C3D, and BIP are the most common – and, if you want free data, you can’t afford to be picky – you just grab it in whatever format it is supplied. However, before you import into Unity, you’ll need to convert all your animation clips to FBX. You may also need to do some cleanup work (in terms of data quality, you typically get what you pay for, so if you’re using data of zero cost you can expect …)

The exact steps required will depend on what format your data came supplied in, and exactly how messed up it is, but here’s some steps I found useful:

 

Cleanup BVH files using BV Hacker

If your mocap data came in BVH format, the first thing you might want to do is use DaveDub’s free BV Hacker tool to load the file and play the animation it contains.

In addition to previewing the animation, you can also edit the translation and rotation of every joint in every frame using the simple sliders on the right hand side. There are also a handful of helpful functions to fix common problems:

• If your character appears to be “floating” above the ground surface (often with a white shadow underneath) for the entire animation, you can fix this with the No Offset button.
• If you want your character to remain on-the-spot for the entire animation (if, for example, you want an in-place walk cycle so you can manually control the actual locomotion of the character), you can check the Centre button and then Clamp translation in X, Y and Z axes.
• You can use the crop marks and the “Knit Ends” option to create a smooth loop animation.
• You can also resample the animation and adjust the frame rate.
• Be sure to take a note of the total number of animation frames shown in the timeline at the bottom – you’ll need this in the next step.
• Once you’re happy with how it looks in BV Hacker, save the BVH file.

 

Removing animation offset in BV Hacker

 

Convert BVH to FBX with Blender

There are probably other tools that can also do this conversion, but I used Blender.

• Load a new scene and delete all unnecessary objects from the scene (the lamp, camera, and cube) by right-clicking each to select and hitting delete.
• From the File menu, click Import –> Motion Capture (.bvh) and select the BVH file you just saved.
• You may well find that the model appears off-screen, in which case hit [Home] to focus the viewport on the newly imported animation. You should see a skeleton highlighted in orange, something like this:

 

• In the animation control at the bottom of the screen, set the final frame of the animation (shown in the End: field) to match the frame count reported in BV Hacker. (If you don’t do this, Blender will treat the animation as the default 250 frames long, which will either cut off frames at the end of the animation, or insert padding frames).
• You can also preview the animation and make any further changes using Blender’s edit mode.
• Once you’re happy, go to the File menu and select Export -> Autoodesk FBX (.fbx)
• In the Export FBX options panel on the left hand side, be sure that "Include Animation" is checked. For now, leave everything else as default (but you may need to revisit this section shortly if things don’t work right first time), and save the file.

 

Convert BIP to FBX with 3D Studio Max

3D Studio Max is a popular, high-end modelling package, and the BIP format is a proprietary file format used for Biped models created in 3DSMax. Sadly, it seems the only way you can load or convert BIP files to something else is to use 3D Studio itself – no other programs I’ve found can read or write to the format.

Fortunately, you can download a fully-functional 30-day trial of 3DStudio from the Autodesk website so, if you’ve gathered a set of mocap data in the BIP file format, you can use the trial software to convert them to FBX as follows:

• From a blank 3DStudio scene, go to the panel on the right-hand side and select Create -> Systems –> Biped.
• You can adjust various options for the biped model, such as the number of bones in the spine, fingers, toes etc.
• Then click in the main viewport and drag to select the height of the created biped – a skeleton model will appear as shown below:

• Now, Click on the motion tab and, underneath the Biped options, click to Load File icon. In the File Picker dialog that appears, select the BIP motion file you want to load. You can choose either to map the animation to the biped rig you just created, or alternatively change the biped rig to match that in the animation – the choice is really up to you, and depends on how much fidelity of the original mocap you want to retain, compared to how well you want to create a skeleton that matches your intended target 3d model.

 

• You might find that loading the BIP file repositions the biped model in the scene, so click [Z] to refocus the viewport on the model.
• Use the timeline scrubber or animation controls at the bottom to run through the animation.
• If you’re happy, select File-> Export Selected, and select Autodesk FBX format. Make sure that “Animation” is checked in the FBX export options – you don’t need to include anything else:

 

Step Three : Import FBX to Unity

• Once you’ve converted your mocap file to FBX format using the steps above, drag it into your Unity project and select it in the Project explorer. In the Inspector panel, it’ll initially look like this:

 

• Click on the Rig tab in the inspector panel, select Animation Type: "Humanoid" and Avatar Definition: "Create from this model", then hit Apply. This will attempt to automatically create a Mecanim rig from the skeleton data in the FBX file.
• Click configure and check that the rig has been created correctly from the FBX file. The model should show all limbs as green. If so, apply the settings.

• Now, click on the animations tab. If you’re lucky, the animation preview should appear and you can click the play button to watch the default avatar perform the animation in the FBX file. Drag any other avatar onto the window and watch your action be performed by different characters – skeletons, robots, or anything bipedal!

 

Troubleshooting – Model Incorrectly Rotated?

• If you’re unlucky, you may find the animation in Unity has been rotated – facing sideways or down, as shown.

This is caused by the fact that some 3d programs use differing conventions for X,Y,and Z axes. I find the problem most commonly occurs (although, strangely, not always) in FBX models imported into Unity from Blender, so here’s how to fix that:

• Go back to Blender, and with the animation selected in Object mode (i.e. the entire skeleton highlighted in orange), hit [N] to bring up the properties window and expand the Tranform panel at the top.
• You need to set a value for the Rotation field – I find that most commonly setting Rotation X:90 degrees is what’s required, so that the character is facing the same direction as the z axis (blue), with y axis (green) going up, and x axis(red) to the character’s left, as shown in the below:

• IMPORTANT: Once you’ve set the rotation, you must then Ctrl-A in the main viewport and click to Apply the Rotation.
• Now, go to the File menu, and once again export the file to FBX. However, this time in the FBX Export Options, change the axes to match the rotated model – in this case that would be Z Forward, Y Up.

• Now, re-import the FBX file into Unity, re-rig the animation and try the preview again. Hopefully the avatar will be standing up, facing the camera. You may have to experiment with different rotation and axes settings before you get it right.
• Once you’ve built up a library of animation clips in Unity, you can then use the MecAnim Animator component to act as a state control mechanism to animate your character between them. But that’s for another post…