[popcornmix]

Tested the same files with 411b and all look proper (aspect-ratio-wise). Again aspect ratio switching doesn't affect actual video but only the masking, I assume this is how it is supposed to work on 3D?

The Pi firmware only allows a single display rectangle to be specified. This allows any zoom mode on a mono image, but only limited zoom modes on stereoscopic.
To handle this when in stereoscopic modes, we disable any custom zoom settings.
This works fine for 16:9 square pixel videos on a 16:9 display (which my collection of 20+ 3D videos all are).
But when this is not true it's hard to handle this correctly.

Last night I bit the bullet, and tried to solve this properly. Basically allowing two zoom rectangles to be specified to firmware.
This should allow all custom zoom modes with 3d contents, including things like viewing SBS video in TAB mode.

I've carefully gone through all the zoom modes on different 3D content using xbmc on windows as a reference and making sure it all matches.
It's looking promising, so hopefully can be pushed out later today.

(I'm still not convinced that all zoom modes possible are sensible. Zooming in to remove black bars for example will change the eye separation and so the depth effect.
But, I think we should match behaviour of xbmc on other platforms).