Surprised at GPU rendering result...

Maverick wrote on 10/25/2012, 11:26 AM
Today I downloaded an update to the Catalyst Control Centre.

On checking V12 Video preferences I now see that there is an option for GPU acceleration selected (prior to the upgrade it just showed as 'Off')
[IMG=http://i47.tinypic.com/110hpua.jpg[/IMG]

I set about a small test on a section of timeline containing AVCHD footage (1920x1080@50fps) of 49 seconds and 31 frames. First with GPU off then with it on after restarting V12 each time.
The section contained 1 fade, a couple of cuts and around a third had it's speed doubled and was rendered to AVCHD 1920x1080, 50fps, bit rate 16M and Video quality at best.

With GPU off in preferences and set to Auto in the Render as box it took 3:28.

With GPU on in preferences and Use GPU if available in the Render box it took 3:32!

I then did one more test with GPU off in preferences and Only use CPU in the Render as box. This time it took 3:20.

Does this mean that setting GPUT if available in the Render as box overrides what has been set in Preferences?

Comments

JohnnyRoy wrote on 10/25/2012, 12:48 PM
> "Does this mean that setting GPUT if available in the Render as box overrides what has been set in Preferences?"

They have nothing to do with each other because they control two completely different things. The GPU acceleration in the Preferences is for accelerating timeline processing. The GPU in the render template controls using the GPU for encoding (that is compressing the actual rendered file). You can turn them on and off independently and it's important to understand that rendering includes timeline processing so you should have them both on for maximum benefit of processing the video on the timeline and encoding the file.

~jr
Maverick wrote on 10/25/2012, 1:04 PM
Thanks for that explanation.

Still seems strange, though, that the CPU only render took less time than the GPU one.
ritsmer wrote on 10/25/2012, 4:06 PM
It seems that the CPU and GPU do not work much in parallel.
If you watch the CPU and the GPU usages during rendering you will see that when GPU assist is ON then some GPU-able functions (like some transitions, FX's etc) are sent to the GPU for processing. So the GPU usage increases but at the same time the CPU usage decreases because the CPU just waits for the GPU to do its calculations.

Now, if you have a fast graphics card and a relatively slower CPU, then GPU assist will give faster rendering than CPU-only - and vice versa.
Zeitgeist wrote on 10/25/2012, 10:05 PM
My test show there is some overlap between the two gpu controls in Vegas 12. Maybe this is the reason for some of the render bugs.
VidMus wrote on 10/25/2012, 10:43 PM
"You can turn them on and off independently and it's important to understand that rendering includes timeline processing so you should have them both on for maximum benefit of processing the video on the timeline and encoding the file."

That would explain why having the GPU=On in the preferences will greatly improve the rendering speed of Mpeg to DVD Architech wide-screen when it does not have a choice for CPU or GPU for rendering using GPU type filters.