1) Set Aspect Ratio Correction in advanced options + set Window > Crop in the right click menu during playback
The Advanced option Aspect Ratio Correction gives you the ability to have a global always-on option to influence the image aspect ratio in a certain manner, eg. exactly compensate for your lens ratio - and in a safer manner too, independent of the videos actual content or aspect ratio.
It was originally designed for older anamorphic screens, but those exhibit the same properties as using a lens.
Overall this would be the best option to use - of course that falls apart when you are talking about per-video usage, more below.
2) Don't see any advanced options, use the Window menu only with Stretch + Crop Black Bars > Video within Black Bars is 2.35
"Stretch" is a bit of an aggressive solution and only works right if the video happens to have the right size - which in this case you ensure by using Crop Black Bars, which will always create an image with the specified aspect ratio.
Stretch has no logic to check for any size or aspect ratio, it'll simply fill the entire screen with the image you have. It can work, but beware those caveats, as it can also screw up if used incorrectly.
The confusing part are the Crop/Stretch options at the top of the right click > Window menu, they seem to behave like they apply to black bars but there is a separate menu item below which is called Crop Black Bars so I'm not sure what that top option does.
Thats mostly coincedental. They would impact JRVR-generated black bars of course, because both Crop and Stretch are designed to not generate any and rather fill the screen instead. But they would not usually impact video-encoded black bars, unless you use the Crop Black Bars option ("Crop" can impact encoded black bars, depending on your actual screen layout and the video properties, but it would only do so if your screen aspect ratio is wider then the video aspect ratio - I should make some explanatory images how crop and stretch impact the image)
Is there a reason why one of these options is better than the other (with respect to PQ)?
PQ is the same, as long as you arrive at the same target video rectangle. All these just calculate source and target rectangles that the renderer uses.
1) some users (e.g. me) have the lens on a slide so it's only in use when required, this means AR/crop changes have to be applied on a per title basis
Do you actually modify the lens settings manually, or did you use madVRs automation for that? I'm not sure if we would re-create something like that anytime soon.
2) a lens is (obviously) a physical device which is present in a single location so this config has to be able to vary on a per client basis
I don't think video playback settings are synced across devices, but i'm not 100% right now.
3) pushing this config into zones would be fairly terrible because it would mean zones are used for 2 things that can vary independently (DSP, video config) which is gets ugly to manage (unless zones get smarter and let you combine different pieces of configuration in reaction to different rules, e.g. something like { if AR > 2.2 apply video zone 1, if channels < 6 apply audio zone 2 } )
Maybe we can move something of this into JRVR profiles once those become a thing, which would also be nice as to have it in a per-monitor section in JRVR, although right now its independent of JRVR, so i'll have to think about how to best do that.
Ideally what I think would work is if we have the ability for JRVR to control the Aspect Ratio Correction based on its per-device config, as well as JRVR profiles. Combine that with a future feature to automatically find and crop black bars, and we should be all there. That'll require quite some shuffling of features though as the Aspect Ratio Correction needs to move some of its logic around.
Per-device solves any concerns of using different screens, and profiles would let you do it on a per-file basis.
Guess I'm back to working on profiles as the next thing, and we can make use of those later for all these things. The conflict of zones with audio settings is why I want to do JRVR profiles independent of zones in the first place, because zones are rather rigid and should probably mostly remain relegated to audio or high-level settings outside of JRVR's domain.