There is an extra scanline at the top of the NTSC signal that tells the CRT TV whether or not the output is interlaced or progressive. For a 60 fps signal, this extra scanline is filled once per 2 frames, such that 30 times per second, 525 scanlines are drawn: 262 for an A frame, 262 for a B frame, and 1 for switching between A & B.
The NES & SNES use a progressive signal, which effectively cuts the resolution in half, but boosts the frame rate up to true 60 fps, as opposed to interlaced, which is effectively 30 fps by requiring 2 passes to fully draw the "frame."
The mechanism for forcing progressive mode is to eliminate the 525th scanline. This tells the TV to continuously draw A frames only, and never switch to a B frame.
This doesn't account for the full calculation, but it's the general idea behind the faster frame rate as displayed on the tv.
As far as the TV is concerned, nothing is being bent out of the ordinary, because each individual scanline is still being drawn at the same rate as always.
With the full calculation, which I don't have in front of me, the EXACT frame rate for NTSC NES & SNES is a rational number expressed by the following fraction:
39,375,000 ÷ 655,171 = 60.09881389744...
If you use a high precision online calculator and plug in this fraction, you will see that it is a repeating decimal. (The first several hundred decimal places repeat en masse, such that you will see "9881389744" again way down the line.
There is an extra scanline at the top of the NTSC signal that tells the CRT TV whether or not the output is interlaced or progressive. For a 60 fps signal, this extra scanline is filled once per 2 frames, such that 30 times per second, 525 scanlines are drawn: 262 for an A frame, 262 for a B frame, and 1 for switching between A & B.
(Thread necromancy is a great opportunity to bring up ancient characters to a list of posters.)
This is interesting; I didn’t know that such mechanism existed.
In any case, I don’t know what calculations the site uses today to derive the movie times in seconds, as I have been kept out of the loop for years. A negligible portion of me is immensely sad about it.
I feel like 60.1 is an acceptable approximation at least for NES.
In any case, I don’t know what calculations the site uses today to derive the movie times in seconds, as I have been kept out of the loop for years.
https://tasvideos.org/PlatformFramerates stores all platform framerates used by the site. How the site derives times is explained on that page (surprisingly very detailed in that regard).
For NES, 60.0988138974405 FPS is in fact used for most publications. Most publications using 60 FPS would just be really, really old legacy movies that used 60 FPS (generally with Famtasia or FCEU, that kind of old, around FCEUX the framerate was switched over it seems), whose framerates aren't stored in platform framerates (framerate was just derived from the movie time when the site data was imported from the old (previous) and new (current) site, a needed step as the new site does not store movie times explicitly, but rather only a frame count and framerate).
