I'm looking to do some video capture with msi ab. However the 'quality' slider under the 'video capture' tab seems to be stuck at 85%. I have tried changing it in the .cfg without avail. I have tried several different Video Formats and Containers, also without avail.
Try a different video format. RTV1 and MJPG allows you to set 100%. I use QuickSync which lets me configure the video quality settings within the external plugin section using "Configure" which will be the same for your CPU/GPU's hardware acceleration mode.
Peek into context help for quality adjustment slider. It is clearly saying that it is only available for MJPG, RTV1 and some external VFW codecs.