Motion Vectors Pre Renders

Hiya, I have been looking to see if pre rendering the motion vector method ie in the ‘Controls’ tab in the Motion Vector Map, using Forward/Backward, Forward, Backward. I’ve found that the results differ from the Analysis.

I’ve cached my clip with a motion vector map, then output it from the Action by turning on the Motion vector pass button. Then using that as a front and matte input into a second Action (I’ve put the backwards into the matte, selecting 2 motion vector outputs and turning on the backwards button for the second) and pulling it in as a motion vector map and changing in the control tab from Analysis to Forward/Backwards. Its close don’t get me wrong but its not the same, so my key frames are off.

When I pull the initial cached motion vector pass that was in the first Action I can see it has 8 channels. Is this why its not going to match? Because the pre render way only has 2, Forward and Back. I’ve tried outputting it as a multi channel 8 layer file but its doesn’t have a Motion wrapper so when I pull it in as a Map it says its not recognized as a Motion Vector Map.

My cache time is down when you pull it in with the Forward/Backwards function so it seems like it could be a good way to use the motion vector as sometimes it drops the cache (always happens last thing at night).

Has anyone had any success with the pre render workflow?

I’ve done this before outside action using a motion analysis node to speed up vector work, but this was before you could cache vecors inside action.

You still have to do a secondary cach gor yhe accimulation vectors but it’s much quicker than a full re-analysis.