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pixels, motion, and scripting
david van brink // Thu 2008.01.10 23:30 // {after effects}

Particles Versus Multiprocessing

Executive summary: if you’re rendering a comp with particles, sometimes turning off “Render Multiple Frames Simultaneously” in Preferences:Multiprocessing can improve render speed bloody significantly. In my case, it went from 54 hours (or longer) to 4.

I’m working on a very fun project just now, as part of a pseudoscientific installation at this year’s Edwardian Ball, which is a playful tribute to Edward Gorey, as well as, loosely, the Edwardian period. Kind-of. I’ll be posting about some of the techniques and tribulations of that project imminently.

Meanwhile, I discovered that, in some cases, After Effects’ particles and multiprocessing renders do not mix well!

I’ve got a fairly complicated comp going… you know how it goes. I’m working alone with no real pressure for elegance, so one thing leads to another and I end up with a big malnamed mess of nested comps. But that’s allowed.

I thought, hey, I’ve just upgraded my brand new Mac Pro (now, officially, last-year’s model) to 9 gig, nothing can stop me now. Started the render at 11pm, watched it render a few frames, and it reported the estimated render time as 7 hours. A few minutes later, render time was 9 hours. That’s ok, I’m going to sleep extra tonight anyway.

Morning comes. “‘Scuse me honey, gotta go check my render!”

7 seconds, 200 some-odd frames, have been rendered, and the disk drive is clackitty whirr clacking, and the estimated remaining time is 54 hours! Ugh. That’s about 2 minutes a frame, for this 60 second comp.

A bit of Googling brought to light: a) After Effects will use at most 3 gigabytes, b) During rendering, After Effects will spawn multiple processes, to help parallelize the render, and use more of the available CPU and RAM resources.

And I myself have noticed that, on a comp with Particle Playground, skipping to the middle can be very slow, but rendering the next frame, and the next after that, is quick. Clearly, when you skip to the middle, it has to recompute all the particle motions from the beginning, but going to the “next” frame, it can work from the “current” frame.

When After Effects uses multiple render processes, each process never gets to do its own next frame! It’s always skipping around to the middle. So I tried turning off this multiprocessing feature.

Render time dropped to 3 hours 55 minutes. I left for work, came home, and saw that the render had taken 3 hours 55 minutes. Ta da! Sometimes hurrying slows ya down.

And, oh, I can’t resist showing a teaser of the work in progress. Here’s the 7 seconds, compressed to tiny. Pix out, mo’.

sevenSecondsSm.mov

click for
http://omino.com/pixelblog/content/2008/misc/sevenSecondsSm.mov

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