Motion blur on retimed proxies

[spacematt]

I have a problem with vray proxies with a playback speed greater than 1. See the attached image for a comparison between alembic, alembic via the vray proxy node, and vray proxies. The alembics and vray proxies have been exported with default settings.

In case its not obvious what the problem is, imported alembics produce a properly extended motion blur. The same alembic imported via the vray proxy node doesn't extend the motion blur correctly. An vraymesh is even worse as it doesn't respect the geometry samples setting (9 in this case).

I don't want to use imported alembics, because my scene has thousands, and the export to vray standalone takes hours. The export when using proxies takes seconds but the motion blur is incorrect. Anything I can do to fix it?

This is on VRay for Maya 3.60.05

motion blur test.zip

[hermit.crab]

If you wish to match the results between a VRayProxy (loaded with an .abc) and the animated geometry, you would need to match the subsamples of the .abc export to the geometry samples used when rendering. For example - a step value of 0.05 would give you 20 subsamples between frames; to match that you would need to set a value of 21 (the last sample is first for the next frame) to the Geometry samples in the Camera Override settings (or assign Object properties and control the samples on a per-object basis).

Note that simply increasing the playback speed will not result in more motion blur time because of the lack of samples - you would need to export the .abc with sufficient samples to match that speed. It would be better to export the .abc with more subsamples and afterward slow the playback instead as means of retiming.