rotationDegrees

Clockwise rotation a renderer applies before the picture is shown, in degrees.

Phones write this into every recording they make in portrait, and a player that ignores it shows the whole video on its side. It is a presentation instruction and not a property of the pixels, which is why it travels here next to colorSpace rather than inside size: size is the size the frame is stored at, so a quarter turn produces an output whose width and height are swapped while size still reads the other way round. A non-square pixel aspect stretches the stored width, so after a quarter turn that stretch applies to the output's height.

Real media produces 0, 90, 180 and 270. A renderer draws any other value unrotated rather than refusing the frame, because a picture the right way up matters more than an exact affine transform. A display matrix that also mirrors the picture sets mirrored as well. Skewed matrices are not modelled.