[Coco] Coco game engine demo

Harry Hurst hhos at st-tel.net
Sun Feb 3 19:23:18 EST 2013

> That's interesting and unexpected.  Any idea why they chose 60000/1001
> instead of 60 fps exactly as the NTSC standard frame rate?

I can't find the reference book I would usually consult before addressing
this question, but Wikipedia has a pretty good explanation.


When the color subcarrier was added to video signal a visible interference
was seen on the B&W screens. To get rid of it the field rate was lowered.
It couldn't be much or the old sets wouldn't be able to sync up with it.

And just to split a few hairs ;D , the actual field rate can be calculated
by dividing the color subcarrier frequency, 3.579545 MHz, by (227.5*525),
which is exactly 1,431,818/47,775, or ~29.97 fps. The frame rate is double
that, at 2,863,636/47,775, or ~59.94 Hz.

BTW the interference pattern can still be seen at times. Try taking a
picture of your television screen (CRT, not LCD, LED or other state of the
art screens) and you should be able to see it, unless your camera filters
it out, as some do.


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