Hi,
I'm have a volume based off the billowy smoke shelf, around 300 voxels (max axis), then converted to a VDB containing density, vel.x, vel.y and vel.z and then cached out.
I load this back in and apply the Retime SOP at 0.2 speed, for a section that I like (frame 100-150), with Advected blend mode and Cubic interpolation.
I've played with many different settings but cannot seem to get a smooth retimed smoke. I'm always encountering judder such as can be seen here:
https://giphy.com/gifs/uFmM2FnFJwNcNWu6gs [giphy.com]

I've seen the retime smokey shoe example by Ben Watts, where he has claimed to have just used defaults settings with advection, but I've tried this a few times on a bunch of sims and I'm always getting problems, most commonly the jittery motion above.

Any ideas where this is going wrong?
Much appreciated
Cheers
J

Here is another example doing a similar thing but a different sim, different computer: https://giphy.com/gifs/69EhNTJHxxpfE6vHU8 [giphy.com]

Nobody has any thoughts on this?

Bump also would like to know.

The skipping cd issue is probably due to a resizing simulation boundary. Here's one that works. 3 frames retimed to 240 frames.

As goat suggests, this seems to be an issue with the bounds.

Putting a volume resize node in after the volume (before my convert to vdb) and inputting a regular bounds node (with some decent padding) into the second input fixed it up for me (rendering in redshift).

An additional follow up, I was specifically getting this with Redshift. I reported the bug and it is hopefully fixed for the next release…

Hi,

I think that I’ve found why this happens, and it is related to the fact that in your scene the velocity grids are the first ones in the primitives list and they have a variable grid resolution among the frames. I’ve have added a fix for this issue to the next Redshift 3.0 build that hopefully should resolve this problem.

Thanks for reporting this issue!
-Juanjo