Increasing render speed by skipping sync (Cycles)?

Support Lighting and Rendering
#1

Hey - I don’t have a fancy GPU Cuda thing. I’m only using my CPU for rendering.

So, I observed that when I use the Render Mode in the Edit Window, cycles syncs the objects. But then if I move around, when the image re-renders, it doesn’t ever sync ever again. This is wonderful - because it saves time. So, I can get a beautifully rendered scene, move around it, and without having to re-sync, it all renders pretty fast.

However, when I render an actual animation, I notice that cycles syncs the objects for every single frame. So, of course, the render time is much, much longer.

So here’s what I was thinking. If it is unnecessary to re-sync the objects when rendering in the Edit Window, it should likewise be unnecessary to re-sync the objects for each animation frame. 1) Why not just transfer that capability to the actual rendering process? I assume, the syncing information could be saved and re-used in the other frames. 2) Is there a way to tap into this ability? Can you render an animation without cycles re-syncing every single frame? Or is it perhaps possible to render using the edit window and then capture animation frames there (through some kind of script preferably)?

#2

It’s not an option yet. The sync step is Blender exporting the mesh data to a compatible Cycles dataset. This means subdivisions and all. Right now Cycles has no way of knowing whether or not mesh data has changed in between frames, and therefore my synchronize on every export. A fix is on the to-do list, and adding OpenSubdiv on the Cycles side of things will help with sync times as well.

#3

What about this? I am rendering an animation where only the camera moves, the objects in the scene are motionless, during the whole animation. Is syncing necessary on every frame?
I have a 1200 frame animation saving all frames individually in jpg format (so that if it crashes I can continue with only the rest).
Would it be faster if rendered in video mkv? Would Blender Sync all objects 1200 times or only once in the beginning of the video? What happens if render crashes? is there a readable file that can be added to in the video editor?

1 Like
#4

Use png instead of jpg. If crash during render to video file format, you have to restart. That’s why it’s recommended to render to images.

#5

Sure, but csimeon was asking here if saving to video directly would avoid having to re-sync for every frame, which would be convenient for large scenes where only the camera moves (working on such a scene myself right now)