What are OptiTrack rigid body (TRA) and OptiTrack skeleton (SKL) files?
TRA and SKL files contain a definition of each asset. These files do not contain the reconstructed 3D data. Instead, they are intended for the recognition and auto-labeling of rigid bodies and skeletons. Thus, exporting and importing these files allow sharing the asset information between different Live sessions and Takes.
TRA and SKL files can be exported by File -> Export Rigid Bodies/Export Skeletons, and exported files can be imported by dragging and dropping the files into Motive.