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.

I am looking into this too now. I have just updated to Flame 2023 and the saved cached motion vectors is new to my workflow.

I like to try and keep my Flame archives tiny small and all relevant shot media on the server. So I am looking at trying to take this 32-bit 8-channel motion vector pass off my local storage.

In the past I have rendered out a UV map once I get the motion vector doing what I want but I am wondering how to make better use of the motion vectors.

If I delete them I can always re cache them but I noticed that in the past (2020.3) it could change.

I’ll keep trawling some old posts to see if anyone has already provided an answer and then if not I shall experiment.

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Yeah I like to archive to dropbox too, so those motion vector cache files automatically saving to your batch reels is really annoying. I did a few a while back and it was trying to archive 500GB to my dropbox.

However this is how it seems to work, it caches the motion vectors in action and makes a copy of that to your batch reel. But it’s a copy, so you can delete from your batch reel, and it is still cached in action. And as long as when you’re archiving you don’t set it to archive motion vectors, then your archive will be tiny again.