Nope - fast accel is definitely possible on legal NTSC - and is commonly used in 8-4 rooms where Mario is coming up out of pipe for the fastest few runs on the leaderboard.

The problem with fast accel in MOST stages, is that there's a second or two of black, with no "cues" - so it's nearly impossible to know the exact frame to start the inputs. If you wait until you see the first frame of the level to start your input, you missed it.

It's much easier when mario is coming out of a pipe, like the turnaround room in 8-4. You get a cue of EXACTLY when the first input will be necessary (when mario is fully visible). That's what makes the remaining framerule so hard - 8-1 (commonly called "Pl8-1" from Stuckinaplate) - you have no reference to know exactly when the level will start...

That and it wouldn't actually help in many of the levels because of framerules. Fast accel in 1-1? Great... but you won't actually save time.

The levels where it WILL help are 8-2 (apparently, thanks to the new WR) and 8-1, which has never been done on a run on the leaderboard, but HAS been done in runs which were not pb's

Since you are using other people's content, you should get the OK from each one of them personally before producing your own content that contains theirs.

What was the time of the 8-4 you used?

@linny356 The 8-4 was 44.443 (8-1).

The 8-4 used was from Taven Webb 2002 on a YouTube video. Watching that is what inspired me to make the spliced run in the first place