Ooops, I though, this was fixed in 2.15.29, because the Changelog says:

• Fix incorrect images when cropping without stretch.

But it's a different issue, and doesn't fix the AR scaling of non-square pixel sources.

There's an active thread on the forum about how to deal correctly with a 1:2.75 display AR file with a pixel aspect ratio of 2:1. Tricky. And it appears there is absolutely no workaround within DCP-o-matic.

Bildschirmfoto 2019-11-08 um 15.37.41.png (34,172 bytes)   

Bildschirmfoto 2019-11-08 um 15.37.41.png (34,172 bytes)   

...but looks to be solved with https://dcpomatic.com/mantis/view.php?id=1636

Maybe, although op says "it's not uncommon for anamorphic video files not to have the pixel aspect set correctly in metadata, so an option that takes pixel aspect ratio into account also wouldn't work in all cases."

Yeah, it may be that 'another' custom setting could be useful. I'm always thinking of 'real' examples that can not be scaled properly with the current set of rules.

I mean, we have seen mainstream DCPs in recent years featuring 2.0:1 and 2.2:1 (2.2:1 also being the standard ratio for many classic and latest 70mm releases). Yet, 2.0;1 and 2.2:1 are missing in the preset list.
In general, for all square pixel files, cropping and letter-/pillarboxing is always a possible solution - however, not intuitively. I usually grab a still and count active pixel dimensions. But that is cumbersome for most users. Solved now with 'No stretch'.

We can not correct files with non-square pixels missing anamorphic flag, if they use an aspect ratio not in the preset list. E.g. I created a squeezed 1.37 version of that 2.75 trailer which misses anamorphic flag as a test. DCP-o-matic interprets it as square pixel, and I can only stretch it to 2.39 max - not 2.75. A custom ratio would solve that final puzzle.

Currently, 'Guess from content' chooses the nearest preset aspect ratio, no? Maybe, 'No strech' is now the better option, as it caters for all intermediate aspect ratios as well.

• Carsten

Just to say that I do see this a fair amount, e.g. files which are 720x576 and file metadata says it's square pixels whereas actually it's a PAL pixel aspect (image should be scaled to 16:9 or 4:3).

All fine if you don't need to crop, but if the active picture is a wacky aspect like 2.0:1 letterboxed within it, it's not possible to crop and scale in DCP-o-matic.

As Carsten says, a custom "scale to" option would solve this final piece of the puzzle. Personally, I'd prefer that to be specified in pixels rather than ratio, so you can scale to precisely what you want with pixel accuracy.

Hopefully things are better in the work done for 0001669; let me know if not.