Debug output is of a job processing again, not of you calling the Vapoursynth Preview, so no additional infos. 
=> create a debug output where you try to open the Vapoursynth Preview, check the taskmgr whether vsviewer is running, don't close until it's gone.
I did a quick test (with a 640x320 source):
(using a 4k source doesn't really change the peak vram usage during the initial phase and just seems to increase the vram usage during the processing; and slow things down)
Dan64 might be able to help here. (I posted here trying to get his attention.)
Cu Selur
Ps.: using preset 'custom' and lowering the 'render factor' to 10 lowered the peak usage to 7.3 GB, so that might help
=> create a debug output where you try to open the Vapoursynth Preview, check the taskmgr whether vsviewer is running, don't close until it's gone.
Quote: Which of the settings would have the most impact on reducing VRAM consumption?No clue. Never tested it.
I did a quick test (with a 640x320 source):
- 'very fast' peaked at 14.4GB here.
- 'faster' peaked at 14.3GB here.
- 'fast' peaked at 15.2GB here
- 'medium' peaked at 14.6GB here
- 'slow' peaked at 15.3GB here
- 'veryslow' peaked at 14.6GB here
- 'placebo' peaked at 15.5GB here
(using a 4k source doesn't really change the peak vram usage during the initial phase and just seems to increase the vram usage during the processing; and slow things down)
Dan64 might be able to help here. (I posted here trying to get his attention.)
Cu Selur
Ps.: using preset 'custom' and lowering the 'render factor' to 10 lowered the peak usage to 7.3 GB, so that might help