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Physical - Render time slowly increasing


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I've never noticed this before. I have a scene that is slowly zooming into an arm with hair. However the render times keep increasing between each frame.

So i turned the computer off and restarted the render where it left off (image seq render) and the render time went down drastically. Render was ramping up to 7 minutes a frame. Then I restarted the computer and it went back down to 4 minutes. Then over the course of 12 new frames rendered, its back up to 7 minutes from 4 minutes.


And previously last night I was rendering the first section of the render at it was rendering at 15 to 25 minutes per frame. Restarted, then 4 minutes, Insane!?


Also noticed just restarting C4D does the same effect.


My computer is still fairly top of the line, 1080Ti 12GB, AMD 16 Core Threadripper 1950x, 64 GB Ram, etc.


Questions I have been asking myself, Is there some sort of processor/memory leak happening? I'm not super technical on thsoe subjects, but it does make me wonder. Anyone else experience anything like this before?


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Are there any plugins involved?

If not, I'd say, this could be something to ask MAXON's support.

If you hadn't 64GB RAM, I had probably also asked for the settings of the Picture Viewer and stuff related to it. If you'd be low on RAM, than those rendered images, cached in Picture Viewer might push the system over the edge (make it swap RAM to disk). The number of cached images can be configured. But with 64GB I really doubt that's an issue.

By the way, you are asking this for R18 (in which case MAXON's support might not be of too much help)?


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do you use GI? To avoid flickering iridiance cache and maybe also lightmaps might try to calculate on base of the old frames. the more frames they have to calculate throug the longer. Well that at least was a problem many years ago. I have no Idea if it still is a problem though.

If you restart the rendering at a certain frame it will calculate fast again, but you might get flickering on your new starting frame. you can of corse render overlapping sequences and blend them together.

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That's sounds like something OS / Hardware related.


Are all your Chipset Drivers, BIOS and other things up to date? Have you looked at CPU temperatures during rendering? Normally if something get's slower over time I'd say there's a temperature problem because the CPU throttles itself.

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I'll get back to this thread soon. I got busy.

Plugins - X-particles
Only used Physical render with GSG Softbox for lighting. No GI or any other setting like AO.

I did not check the temps. I'm going to strip down the scene 1 layer at a time and see if its a C4D file issue.


Could be some sort of OS/Hardware too.

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  • 1 year later...

My bet would be on an increasing sample count, basically what Jops proposed. If you break continuity by starting rendering at a later frame you get lower times per frame, but a flickering result. Sadly the OP never answered that.

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Yeah i'm experiencing that as well. I render in batches of 5 frames now. As render times increase rapidly in batches of 10 for example. Havent experienced any flickering as far as ive seen.

But its a time consuming thing and have to check my pc every 20 minutes....

Would be great if you could render out an animation as if all frames were separate stills, but in an automated way.

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  • 6 months later...

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