Question / Help Which Downscale uses cpu vs GPU?

[BigYuckFou]

Hello,

I see there re two ways to downscale. One under Video and one under Stream.

Can someone please help me understand which one uses the GPU and what one uses the CPU? and which I can expect the best quality results from using top end CPU with major overhead and 2080 GPU?

I use x264 encoding as well. Not attempting to offload any work onto the GPU, just want to understand what provides best quality.

Thank you all for any help you provide.

 

[BigYuckFou]

I feel like a dummy, found the answer here. https://obsproject.com/forum/threads/downscale-vs-rescale.72172/

anyone have anything to add I am all ears since that post is three years old and things may have changed.

 

[carlmmii]

That description still holds true. For conciseness' sake, the only time CPU rescaling is done is when the "Rescale Output" option is selected in the output settings. This also has the side effect of silently reverting to the old Nvenc encoder if Nvenc (new) is selected, because the composited frame has to be sent from the GPU to the CPU, and then back to the GPU, meaning the direct VRAM->Nvenc path cannot be used.

Btw, this may seem somewhat obvious, but it is rarely mentioned when this topic comes up - any scaling done on sources within the canvas does use the GPU, and also has options for which rescaling method to use.

 

[BigYuckFou]

Can you tell me, if I choose NVENC encode (new) and use the rescale under output, does it still use the CPU?

 

[carlmmii]

Yes, it will. It will also silently revert to the old Nvenc encoder.

 

[BigYuckFou]

boy oh boy. silently. that tears me up inside. :(