smplx_anim_to_alembic

SMPL-X Animation Data Preparation for Unreal

This tool lets you batch convert a folder of BEDLAM SMPL-X .npz animation data files to Alembic ABC format using ❤️Blender❤️.

We later import these ABC files into Unreal but they can also be used in other tools like Blender. Blender import and playback of ABC is very fast.

Note that the SMPL-X pose correctives are baked in the Alembic geometry cache and will be automatically applied when playing back the Alembic files after importing. Additional plugins do not need to be installed for proper playback.

Requirements

• Windows 10 or later
  • Data preparation stage will likely also work under Linux or macOS thanks to Blender but we have not tested this and are not providing support for this option
• Python for Windows (3.10.2 or later)
• Blender 3.2.2+ for Windows
• SMPL-X Blender add-on (20220311 or later)
  • This tool will let you import BEDLAM .npz animation file into Blender as animated female/male SMPL-X (v1.1) mesh
  • Installation instructions:
    • Register at https://smpl-x.is.tue.mpg.de and download the SMPL-X for Blender add-on (300 shape components). The ZIP release file will include the required SMPL-X model which is not included in the add-on code repository.
    • Follow instructions at https://gitlab.tuebingen.mpg.de/jtesch/smplx_blender_addon

If you want to use the BEDLAM animations:

• Download BEDLAM .npz animation files from https://bedlam.is.tuebingen.mpg.de and extract to your filesystem
  • SMPL-X gendered (gendered_ground_truth.zip)
• Extract .npz animation archive to your filesystem
  • Example: C:\bedlam\animations\gendered_ground_truth

Usage

1. Edit smplx_anim_to_alembic_batch.py and change BLENDER_APP_PATH to point to where you installed Blender with the SMPL-X Blender add-on
2. Open Windows command prompt where you have access to installed Python 3.10
3. Run multiprocess batch conversion. The following example uses 12 CPU cores. Depending on your available CPU core count and available main memory (128GB+ recommended) you can increase or need to decrease the amount of processes. For fastest processing make sure that you have a fast SSD with large enough space (512GB). On a fast system processing time is around 20h for whole animation dataset when using 12 cores.

Example:

py -3 smplx_anim_to_alembic_batch.py C:\bedlam\animations\gendered_ground_truth C:\bedlam\abc 12

Notes

• BEDLAM .npz files use Y-Up format in SMPL-X OpenGL coordinate frame notation. To properly manually import them into Blender with the add-on you need to make sure that Format:SMPL-X is selected in the import dialog. Also enable SMPL-X pose correctives by activating Use keyframed corrective pose weights. The Alembic conversion automation script (smplx_anim_to_alembic.py) is always using these options while it is running.
• If you want to import AMASS SMPL-X .npz animations with the automation script you need to change smplx_anim_to_alembic.py to use anim_format="AMASS"
• If you want to play the 30fps ABC files in Blender then make sure that your Blender framerate was changed to 30fps from the default 24fps before you import the file. We recommend to change to 30fps once and then save as default via File>Defaults>Save Startup File.