Preview vs. Render time vastly different - Any ideas?

Forum|Forum|2 days ago
February 23, 2026
3 replies
49 views

I have a fairly complex and large scene. I accept it’s going to be slow, especially with my system specs. I have been working on it in quarter res and it can easily preview render that.

But what I can’t get over is the render time!

A full quality preview takes 15-25 seconds to render a single frame. This is somewhere I would expect the final render to be. It doesn’t matter where I put the play head on the timeline it’s always between those times to preview a frame.

When I start rendering, it seems to be around this time, but then it starts getting really slow.

I have switched from ProRes to a PNG sequence to try and figure how long this is actually taking and where it’s slowing down and the results are...interesting.

At a point during the animation it goes from slowly getting longer per frame (each frame is taking up to a minute or so) to suddenly getting really long per frame, each frame is then taking around 15 minutes longer than the previous, and now I am up to over 2 hours per frame. There seems to be an exponential growth in render time at a certain point in the animation for no obvious reason. I could understand this might happen over the 20 minute scene, but not within the space of 10 frames (seconds to hours)! At 25fps, you can imagine the difference between one frame to the next can’t be THAT significant to change the render time that much.

I can absolutely accept a difference in preview vs. render times, but a 40,000% increase? And if I leave it, how much higher will it get?

I have disabled GPU acceleration to see if that helped, it didn’t. I have tried it both with the AE render queue and Media Encoder with no real difference.

I have tried it with or without DOF, with or without motion blur, with or without lighting. They all make a difference to the preview render time (around 5 seconds max), but don’t really change the actual render time.

As I said, it’s a complex scene, it’s got to be thousands of shapes being processed and a camera flying through them. I expect it to be heavy, what I can’t get past is the preview to render time differences.

Has anyone got an experience of this kind of problem?

FYI: Due to the scene, pre-rendering is next to impossible. The only thing I could do is multi-pass the scene with different passes and piece it together, but as the scene has elements happening around the camera and between each other, I would need to also render depth/opacity masks for each run and I am not sure if I can do that out of the box in AE.

PC:
Source materials are on one NVMe, rendering to another NVMe.
CPU: 12900H
RAM: 32GB.
Latest AE (26)

EDIT: For clarity, this is a brand new project in AE 26 created in the last few days as a clean installation. It’s not using any 3rd party plug-ins.

ToolfarmJP

Community Expert

You launch the Task manager when you render it. You can check and see which part (CPU, Disk access, Physical memory, etc) is heavily loaded. You improve the part.

C

CynetixAuthor

Inspiring

That’s the thing, it starts off using quite a bit, but then it drops. It’s basically background at the moment, even though it’s supposed to be rendering.

The Firefox process I am writing this reply in is using more CPU and RAM.

R

Rick Gerard

Community Expert

Fifteen to twenty seconds per frame is not horrible, unless your comp is not extremely complex. I occasionally render 4K composites with hundreds of layers in the render nodes, which can take a couple of minutes or more per frame. The same thing can happen in DaVinci or Fusion, and don’t even get me started on rendering in 3D apps.

Tell us a little more about your comp, show us the expanded flow chart and maybe we could help you clean up and simplify things. I would share a flowchart I posted a while ago if we still had access to our uploaded files, but sadly, that feature is now missing from the forum.

C

CynetixAuthor

Inspiring

Hi Rick,

I don’t consider several minutes long for a frame render either.

It’s more that a preview of any frame in the scene takes 20 seconds (at full quality), but at render time it got progressively slower as it goes and was taking 2 hours a frame when I gave up. When it decided to render 5 frames it never finished them, it was almost like it locked up (but didn’t).

I ended up re-saving the project for AE 25, installed that and although it slows down, it’s got beyond the same render in 26 and it’s only taking an hour a frame at the moment.

There is obviously something wrong with the comp or I am triggering a problem with AE that is there in 25 and 26 (understandable). But one thing is for certain, 26 is slower at rendering than 25!

I disabled the cache compression in 26 which helped, but there is no two ways about it, 26 is slower.

So, my current setup.

I am working in 4k, but downscaling to 1080p before rendering. This is just to give me the scope to increase the resolution later on if required.

I built this with far more expressions than I usually do, mainly because it’s very repetitive and I couldn’t be bothered to hand animate it all. So it’s possible that is causing render time slow-down, but it’s fine in previews.

The Scene:

The camera simply moves along the Z axis for 20 minutes and the POI is scripted to look at around 200 different images as the camera passes them. There is easing, but this is handled by an expression. The camera is using DOF.

The images are distributed through 3D space, again with an expression.

The images a pre-comped and designed to look like Polaroids. So each image comp has 2 layers and most images have a simple sharpen running on them. Most images are PSD’s with a variety of things going on, all operating on smart layers. These images were interpreted as flat footage and no layers.

There are 2 lights, a omni that is parented to the camera and acts like a camera light, illuminating what the camera is looking at as it gets close enough. The light is not casting shadows. The second light is a low powered fill light.

There is a flat background behind the whole lot, but this is not 3D.

The big killer is the “dust”. I am almost certain this is where the problem is. To help show the camera looking around there are “particles” floating around like dust, they are scattered around the scene and along but fairly contained to the area around the camera, but all along the Z axis.

As the scene is so big, CC Particle World can’t get close to filling the scene, there is simply just not enough scope in the Z axis, both in size and positioning. So I decided to build the particles manually. I created a “dust” comp, which is basically a flat coloured circle shape, and added to a “particles” comp. The dust comp is 3D and duplicated 500 times. Each one has expressions on them that randomly positions it within 3D space (X, Y and Z) and randomly sets the opacity. The particles comp is then added to the main comp and has collapse transform enabled. It is then duplicated 60 times and they are stacked end to end along the z axis.

This creates the particles in the scene, but they are heavy on the CPU.

That UHD comp is then added to a 1080p comp and scaled to fit. I then add a bit of grain at this level to help sell it and export this.

I haven’t used Trapcode’s Particular in years, but that may be a good replacement for the dust...but that requires spending money 😁

C

CynetixAuthor

Inspiring

I am not saying it’s helping, but I have just tried the suggestion from this thread:

To disable cache compression.

“ In Preferences->Disk there’s a new setting which compresses cache files to save disk space, which is enabled by default when updating to 26. I’ve found this to be a huge detriment to performance. Try turning that off.”

If nothing else has happened, AE’s CPU utilisation has gone up, the fans are running harder and more cores are in use. It’s possible multi-frame rendering is now working when it didn’t seem to be before.

AE isn’t showing any difference, but I’ve now got circa 8 cores running hard instead of 1 being slightly busy and the rest ticking over.

EDIT: Yep, I’ve got 5 frames being rendered simultaneously according to the PNG files in the export directory. Previously it was doing one a a time.

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