With body motion tracking, can a dev specify the sample rate of the sample (every few ms) and write out that sample in a continues manner. eg a basic motion recorder. Please ignore the question if this is the wrong place to ask
Body tracking runs at 60 Hz at the same cadence of the camera. We cannot compute this faster than this. However, by changing the ARVideoFormat you may change this to 30 Hz or other supported frame rates.
We do not offer a functionality to write the motion capture data to file. However, our data is very well compatible with a format called BVH. By following the topology of the skeleton given by the ARSkeletonDefinition and the data coming from an ARBodyAnchor one could generate such a file output.