HELP! Slow motion shot approach

[Jesper Rahlff]

Hey guys.

how would you approach a slow motion shot?
I have to do a fluid sim, which has to be slowed down drastically.

so here is the information I have available:
I have a raw plate which is 1600 frames long super slow motion.
The plate is being retimed to 129 frames in nuke.
After the retime the first 35 frames is normal speed, and then it slows down until it hits the slowest point available with the fps it was shot at (speed of the raw plate).

 

So far my initial thought is to Sim the whole thing to the raw plate and then apply the retimed curve afterwards, but I have such a hard time getting my sim to look correctly when I sim it this slow, and also that means I have to sim 1600 frames.
The other thing is that I have currently slowed down the timescale on the Dopnet for my sim to get it as slow as I need, and as soon as I do the look on my sim totally change. I figured it is because the timescale is not truly a timescale that can be used for this, but this is as far as my knowledge goes with regards to slowmotion stuff. 

 

So is there anyway I can sim at regular speed, so I maintain proper force appliance etc (timescale 1 on my dopnet) and then extract some kind of information (I am thinking substeps maybe?) that can give me the in between frames information (maybe @P?) and then slow it down that way?

 

let me know what you guys think, or which approach you would use for something like this.

 

Cheers

 

[woodenduck]

My first thought is to do the exact opposite. Sim the fluid at normal speed to get the desired behaviour. Cache that to disk. Read the cache back, add a Timeblend Sop followed by a Timewarp Sop. 

slowMoFlip.hip

Edited May 6, 2016 by woodenduck
Added example file

[woodenduck]

Don't forget to turn on 'add id attribute' on the flip solver or the Timewarp will run in to problems. ;D

[Jesper Rahlff]

Thanks you so much. This approach works perfectly for what I need to do.

You just saved me 3 weeks of RnD on this Joe! You are the best.

 

Cheers

[Jesper Rahlff]

So I was able to use this approach for what I needed to do. I will however say for people who might be reading this thread with similar questions as I had, this approach becomes a bit more tricky if your source emission of the fluid is in frame during the shot.
By default emission happens once per frame, and will be the desired amount based on your input values. When you retime the fluid the motion will slow down to 1/n (n being your value), but this also means that you have to create a work around and get Houdini to emit fluid on a 1/n'th frame basis instead of a per frame basis. otherwise you will have a steppy emission that only creates new fluid every n'th frame.

hope this helps.

I will post an example file around this as soon as I find a solid way of doing this. So far I have ran into other issues that is not necessarily an issue you would prefer over steppy emission.

If anybody have any suggestions of how to overcome this problem, let me know.

cheers

[dimovfx]

I know that this can be ridiculous but you can try changing the FPS to something high, like if it was shot with high speed camera