I would like propose a new "framesPerSecond" standard attribute
for OpenEXR:
The attribute defines the frame rate at which an OpenEXR image
sequence should be played back. All frames in a sequence should
have this attribute, and the attribute's value should be the same
for all frames. If no frame rate is specified for a sequence,
then playback software should assume 24 frames per second.
The attribute's value could be represented either as a floating-
point number or as the quotient of two integers. A floating-point
number would be easier to use, but it cannot represent NTSC frame
and field rates exactly. A quotient would be slightly less
convenient, but all commonly used frame rates, including NTSC,
can be represented exactly.