GPU and CPU encoding loads with effects

Report · Feb 22, 2019

Alright, so correct me if I'm wrong here, and if I'm wrong, would be nice with some explanation.

So I have this 20 minute timeline I'm currently rendring/encoding to h264 with Media Encoder and CUDA on.

The timeline consists of A LOT of 200fps .R3D clips time mapped so it's realtime in a 25fps timeline. The footage is a variation of 3-5K, downscaled to 2K (2048x858 due to 2.40:1 ratio).

I have the dust & scratches native premiere effect on almost all clips (dirty lens) and with an adjustment layer that consists of a simple grade/color correction on top of all clips.

So to the actual question:

When I rendered out a preview of the timeline, I get rendertimes down to around 11minutes, seeing my CPU load is between 70-95%, and my GPU load is around 30-60%.

Now when I'm rendring with the scratch & dust effect on the clips, (and yes, I know I'll get longer encoding/render times due to the effects), I see that my rendringtime is around 40minutes, CPU load is around 95-100%, but my GPU only uses around 10-15% ??

How come that adding a effect like scratch & dust makes an impact on how it's rendered between the GPU and CPU? In my head it should only "add more stuff cpu/gpu has to do" in other words, lets say that the GPU would need to work around 60-80% load?

I have a newly built Threadripper 1920x, 32gb DDR4 3600mhz, SSD's with an 2080ti, which is more than capable to render heavy stuff, I just don't understand why it's not that efficient when adding that effect..

Best regards

Report · Feb 22, 2019

Just to be clear: are you talking rendering timeline as in making preview files or export timeline?

Your timeline might be using a different codec to render preview files opposite the codec used in the export.

Different codec, different workload.

Report · Feb 22, 2019

Sorry for the confusion.. I'm talking about the actual export of the final timeline. It's the exact same files getting exported from AME. So it's not really about the encoding time, because even I can understand that more effects equal longer export times.. It's more about the workload on the GPU/CPU with effects that confuses me.

Report · Feb 22, 2019

Scratch and dust is a cpu effect only.

That would explain the workload on the cpu.

I dont know why the gpu drops, are you using preview files?

Report · Feb 22, 2019

For this particular RAW cut project (basically just dumping a lot of clips that was not used in the main project) I'm not really using preview files afaik. Rendered the timeline without scratch and dust first, then with scratch and dust afterwards. Don't know if it uses preview files after that (have "use preview files" enabled in AME)

It's not a big deal for encoding times, nor is it really a problem for me. I just need to understand why the GPU drops, since it's clearly good to have the GPU helping for better encoding /exporting times.

Report · Feb 22, 2019

If your render bar is green and you have Use preview files checked in AME then you are using preview files.

Using preview files is only usefull when export codec is the same as the codec used in the sequence otherwise you might end up with a file made by a lesser codec.

Using preview files off loads the workload.

Report · Feb 22, 2019

That I understand, but it still (no offence) doesn't answers why the GPU load drops when adding a simple effect, where it actually should rise imo.

Report · Feb 22, 2019

Look at the lego-blocks to the right for any effect in the Effects list. If you see one for GPU use, that effect uses the GPU. If there is no GPU Lego block there, it's only CPU processed.

You keep talking about rendering a timeline then doing something else, so I think there is still miscomunication here. Export means you create a new file to a location on disc, which you could re-import or view elsewhere. Render meanscjustvto make previews of parts of a sequence for use in playback within Pr only, probably does not make even a complete file, and unless you've changed settings, uses a small low-quality codec.

Neil

Report · Feb 22, 2019

In this case I mean exporting/encoding aka saving it as one file.

Report · Feb 22, 2019

You're adding a pretty heavy non-GPU effect. This means the CPU/RAM work has gone up, and as there are all sorts of timing/sequence of processing things involved in coding for this, I would guess it has slowed down frame processing at least a certain amount.

Slowing down the number of frames processed per second means lowering the need for GPU per second.

Same workload done over the export but less load per second.

Neil

Report · Feb 22, 2019

Neil,

This is something that actually could make sense.. Seeing 20% load when adding that CPU heavy effect, means CPU needs to work more and then seeing it around 40-45% when not added..