TYPO3 Core

The system currently behaves as technically expected at this point - but not as expected by the user.

The aspect ratio is specified with the widely used value of 1.91:1. This leads purely mathematically to the described problem, because:
1200/1.91 = 628.27 => Thus, the cropped image is 628 pixels high at a width of 1200px.
628*1,91 = 1.199,48 => So the cropped image is 1199 pixels high at a height of 628px.
Facebook says "Use images that are at least 1200 x 630 pixels for the best display on high resolution devices." and "Try to keep your images as close to 1.91:1 aspect ratio as possible to display the full image in Feed without any cropping." (Source: https://developers.facebook.com/docs/sharing/webmasters/images/?locale=en_US)
So the correct aspect ratio is not necessarily 1.91:1 but only "as close as possible" to it. Mathematically, 1.9047619048:1 would be correct.

For reasons of clarity, I would configure 1200:630 as the new aspect ratio (alternatively 40:21, as a shortened notation). This even allows to directly capture the recommended image dimensions when reading the code. I guess we can still keep the "name/label" 1.91:1 as it is widely used.

With this, the image then no longer needs to be processed if it is uploaded in the correct aspect ratio. However, a short test shows that processing takes place anyway. A check whether the processing is necessary should be able to solve this problem.

This is a nice task for starters at tomorrow's Coding Night at DevDays. I'll take care of it.

Patch set 1 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/75382

Applied in changeset cbca19cbeb323c0911e6b8c2d08c96eba90cc64f.

Patch set 2 for branch 11.5 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/75358

Applied in changeset b51d0015b2732d869c9845ae38ca5dc938b3bbc9.