Frame rate and screen refresh

Maverick wrote on 1/6/2004, 10:57 AM

This has been troubling me a while so I hope the more knowledgable poeple here can put me right.

I often read complaints that the monitor version of a project differs significantly when viewed on a domestic TV.

If, say, the frame rate is 25fps and the montitor refresh rate is 80Hz then, surely, a screen refresh can occur midway through a frame where on a TV the refresh is the same as the frame rate? Or have I got it totally wrong?

Cheers.

Comments

Chienworks wrote on 1/6/2004, 12:24 PM

I would say you've got it right. The computer monitor refreshes it's display every 0.0125 seconds and a new video frame will be available every 0.04 seconds. So, the monitor displays the first frame on it's first cycle through 4th cycle, then on the 5th cycle it will have a new video frame to display, which it will do for the 5th, 6th, & 7th cycles. Then on the 8th cycle it will be displaying the 3rd video frame ... etc. and so on. There will be a repeating pattern of 3 or 4 monitor refreshes for each video frame.

Of course, this assumes that the video is progressive. If it's interlaced, then it's a bit more complicated. The video will have new fields every 0.02 seconds and the pattern will be somewhat more complex.

Televisions generally sync to the video signal whenever possible rather than using their own refresh rate.