Epiphan VGA2USB Pro - Manual (Page 152)

18. Advanced topics About the frame rate
Page 152 Epiphan Frame Grabber
For the VGA2USB Frame Grabber, n is always 2 (because the
VGA2USB Frame Grabber maximum color depth is RGB16 which
is 2 bytes per pixel).
For the DVI2USB Frame Grabber n can be from 1 to 3 depending
on the capture mode. The DVI2USB Frame Grabber maximum
color depth is RGB24 (3 bytes per pixel) as well as RGB16 (2 bytes
per pixel) and RGB8/Grayscale (1 byte per pixel).
For Frame Grabbers that support hardware compression (the
VGA2USB LR/HR/Pro, DVI2USB Solo/Duo) the maximum real
frame rate very much depends on the entropy (statistical
properties) of the input VGA or DVI signal. In other words, the
frame rate depends on how well the signal can be compressed, or
how much the next frame is different from the previous one. The
frame rate can range, from less than non-compressing VGA2USB
in the worst-case scenario (because the format for compressed
data adds extra overhead) to 60 frames per second (hardwired
limit) if almost nothing changes on the image.