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Camera issue every 4th frame when rendering out using the compositing tag

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Keith Banger
Camera issue every 4th frame when rendering out using the compositing tag
on Mar 27, 2019 at 3:10:04 pm

I'm fairly new to C4D so bear with me...

My scene is a boat engine room on fire. I am using After Effects to composite in some smoke and fire into my scene using Trapcode Particular. There are some engine parts in the foreground that the smoke/fire moves behind as the camera moves, so therefore I need to composite these effects in-between and just on top.

What I have done is rendered out the full scene (with moving camera) as a png sequence. Then, using the compositing tag I have rendered out just the front half of the engine with an alpha channel (also as a png sequence), and placing that over top of my full sequence in AE, creating a top layer which I can then add the fire and smoke effects under. In theory it works perfectly and in previous attempts of this I didn't have the issue below.

My problem is that every 4th frame of the top sequence for some reason doesn't line up. Its like the aspect ratio or camera angle in C4D changes ever so slightly for just that frame, then back to perfect. I've included 3 pics (in sequence) to show what is happening.

The render settings are identical, same camera, all that. And I've re-rendered out each clip with same issues

Thanks for your time!

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Steve Bentley
Re: Camera issue every 4th frame when rendering out using the compositing tag
on Mar 27, 2019 at 10:46:44 pm

First check the camera that you are viewing the C4D scene through (the active camera with the white checkbox in the object manager). Its also good practice to turn off or delete cameras you won't be using so the wrong one doesn't get exported.

The render doesn't really need the external compositing tag, that's more for when you bring the data into AE. (assuming you are rendering out of C4D and not letting AE render the C4D stuff for you.)
You do need to bring the exported data from C4D into AE so that you have a camera that is the same (and the position of the objects). But the renders are just frames or movies that are "flat" and fit to your comp window in AE.

Make sure you comp size matches your render size in C4D and your frame rate in both C4D and AE - 29.97 is not "close enough" to 30. Make sure your aspect ratios match too.

Are you using any motion blur in either C4D or AE? If so, try a short render without and see if that helps.

Make sure to turn off any cameras you had in AE and only use the camera that came in from C4D.
Make sure you are in camera view in AE and not one of the other views available (front, Axon, Iso)

Failing all that, if you can trim the C4D project down to just the camera and the objects that aren't lining up and trim the AE project down to the same, you can upload it here and we can take a look.

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Keith Banger
Re: Camera issue every 4th frame when rendering out using the compositing tag
on Mar 28, 2019 at 2:06:43 am

Thank you for the detailed response!

To clarify, I am not rendering any C4D elements directly within AE. I am rendering out the full scene with all elements on (as a bottom layer in AE) and just the front parts of the left "engine" turned on (as a top layer) with an alpha channel as PNG sequences so that I can import and layer them in AE and add Particular in between them to simulate depth. I then use the After effects camera tracker to motion track Particular into the scene (which worked perfectly).

I do not use any C4D camera data-- I tried it for particular and got terrible results-- or anything else from the C4D project for that matter. Just the png sequence exports. And it is one of the exports that does not match the other-- every 4th frame is a little "off" and then matches back up on the next frame.

I have checked frame rate and it is the same camera and frame rate being used for both clips, and the framerate matches the AE composition frame rate, aspect ratio, etc.

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