I don't know about everyone else, but seeing widescreen images sticking out in between vertical posters is very distracting.
I'd be happy with the ability to crop the video frames in to the same aspect ratio. Something simple like:
Clicking the small crop icon would take you to something like this:
The Aspect ratio of the crop box could be locked, and simply drag left to right
And, then Plex would process the image, save a new cropped version, and use that for the poster:
I know that there will be people who want different aspect ratios, or more control, but that quickly gets in to sticky territory, even just from an end-user perspective. People who want more control can always jump over to an image editing program.
This solution fits at least 95% of use-cases I can think of.
