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View Full Version : When switching video output, *what* causes the speed change?



Elusive
04-16-2007, 02:41 PM
I've been pondering this. Modern games that can switch the console's video output from PAL to NTSC if you have a compatible TV set run at the same speed no matter which you choose; the only difference I can spot is the usual screen borders. Mega Drives are identical internally throughout the world besides the language and video hardware settings (besides different board revisions, of course), so why is it that switching video outputs on non-PAL-optimised games speeds up the game? My initial thoughts are that video outputs are tied to processor speed, but that's silly as the processors are identical globally.

I mean, if I put Sonic 1 in a European machine, it plays slower than if I put it in a Japanese machine. It's still the exact same game ROM inside the cartridge, and the exact same console 'guts', the video format is just different. So why the speed change? PAL TV sets don't display a slower image than NTSC TVs.

Joe Redifer
04-16-2007, 07:01 PM
Because the game console would render 100% of the frames in both PAL and NTSC. So in PAL, it takes longer to show all 100 frames (for example) than it does in NTSC. With polygon games it is easier to speed up/slow down the frame rate to match the PAL or NTSC timings without any noticeable difference (it can be done in the hardware rather the software). And I think all HDTVs run at 60fps (some can go up to 100 or 120 fps I hear).

Elusive
04-18-2007, 02:07 PM
I see - I guess that means the alternative to slightly slower PAL games is dropping roughly one in five frames?

Joe Redifer
04-18-2007, 05:48 PM
Basically, yes. Of course that would look very herky-jerky as dropping frames when your mind expects one to be there would not appear smooth at all. But polygon games actually render at 50fps, so the onscreen differences between the frames are 1/50th of a second instead of 1/60 with frame drops.

David J.
04-18-2007, 11:03 PM
I've always wondered why you need a SCART lead for a PAL MD if you want to play in 60HZ?

Another thing, what year did composite video come out on TV's?

Joe Redifer
04-19-2007, 02:10 AM
Composite video has been the nature of NTSC video since it became color. You may be asking when the "composite input" became available on TVs. I'd probably say they started showing up not long after VCRs came out, maybe 1984-ish.

Rawit
04-22-2007, 06:30 PM
I've always wondered why you need a SCART lead for a PAL MD if you want to play in 60HZ?

A PAL Megadrive encodes the color part of the video, corresponding with the PAL format. This means you get a 50hz, 625 line signal, with PAL color encoding. This signal is accepted by PAL tv's.
A modded Megadrive will output the same, except for the signal frequency, which is changed to 60hz. The color encoding will still be PAL, and won't change to NTSC. This signal is non-standard, and won't be accepted by a great number of tv's.
Using a SCART lead to get RGB video from your Megadrive, bypasses the color encoding entirely, and the tv is capable of displaying the 60hz signal with the correct colors.

Joe Redifer
04-22-2007, 07:27 PM
What about PAL 60? Isn't that a format?

j_factor
04-22-2007, 11:17 PM
PAL-60 is just PAL at 60Hz. Most newer PAL sets are capable of both PAL and PAL-60.

Joe Redifer
04-23-2007, 12:01 AM
That's what I mean. Rawit said:

A modded Megadrive will output the same, except for the signal frequency, which is changed to 60hz. The color encoding will still be PAL, and won't change to NTSC. This signal is non-standard, and won't be accepted by a great number of tv's.

Wouldn't that be PAL 60?

Rawit
04-23-2007, 04:50 AM
True, that is PAL 60. Nowadays a great number of tv's support it, but still not all. My LCD tv displays it perfectly, but on my older Philips widescreen I need to use a SCART/RGB lead to get the correct colors, because it thinks the signal is NTSC.
Although PAL 60 is used often nowadays for consoles and vcr's, it isn't an official standard.