Good Q. I could never tell on short renders. The last render started to break up after about 3 days, on a PC which was not touched at all.
Also I don't know for sure at all whether NB is the cause of that render corruption problem. "We" think it might be responsible for it because Pro 13 crashes very fast if GPU is globally enabled (under Preferences), and this NBFX Lens Correction plug-in is the last place in which GPU has not been disabled.
Is there any way to tell in Vegas whether the GPU is being used, in any context? I think it always uses it for the preview window - well obviously because the video card is doing that!
Edit: just doing a render of a 7 min movie, same FX as usual (contrast, colour correction, lens correction), and it estimates 2hrs+ render time. That is about 1/20 of real time and about 1/2 the speed of previous, so it could well be that something has changed.
and it took 2.5 hours which is 2x longer than normal. So maybe the GPU option in NBFX was being used and isn't anymore. But I cannot tell otherwise.
The other thing is that I repeatedly accessed the computer over remote desktop (RDP) and that didn't corrupt the render. It did however cause Pro 13 to crash at the end, leaving the finished .mp4.tmp file there, which I just renamed to .mp4 and uploaded to vimeo.
Sure; a lower bitrate speeds it up correspondingly.
However, the camera produces 25 mbits/sec (most likely fixed bitrate) and I don't want to lose too much of that. If I was doing stuff only for vimeo and then chucking it away, I would render at 5mbits/sec, or maybe 10 because Vimeo does its own downsampling regardless of what you upload, to about 5.
If those stoopid checkboxes could be checked or unchecked, I could test this with and without, but right know I cannot tell if the NBFX lens correction is using the GPU or not.