What's going on here, please?

More specifically, where are the dimensions 1248x702 px coming from and
why is Quicktime Player X displaying at and cropping to those dimensions?
Notes: the image above was composited in Photoshop. The pixel aspect
ratio for the exported FCP sequence was 1:1 (i.e., "square").

More specifically, where are the dimensions 1248x702 px coming from and
why is Quicktime Player X displaying at and cropping to those dimensions?
Notes: the image above was composited in Photoshop. The pixel aspect
ratio for the exported FCP sequence was 1:1 (i.e., "square").