> Don't 240Hz TV's do this automatically. They take a 60Hz picture, interpolate an
> extra frame in between making 120Hz then add 120 frames of black for 240Hz.
> Not saying they take 120Hz in, but they already strobe a 60Hz picture.
That is correct, so it's not MAME's responsibility to do the black frame insertion stuff on this specific TV. It becomes the TV's responsibility. Just use regular MAME. MAME can only do black frame insertion if it has 100% full control of the 120 Hz refresh.
Different TV's do different tricks to create 120Hz and 240Hz. Some of them use black frames and strobing. Others use interpolation. Or a combination of the two. Unfortunately, frame interpolation tricks adds input lag, so black frame insertion is better for video games. Most LCD TV's are not very good at doing zero-motion-blur MAME, you need a plasma or CRT TV instead. One rare exception is the Sony Motionflow Impulse which has a special non-interpolation Motionflow mode on the Sony HX950 series that looks great with MAME. Most Motionflow modes don't work well for games (laggy & artifacts) but that special Motionflow Impulse mode is wonderful for MAME. It is a better black frame insertion that does a good 75%:25% dark:visible ratio, which reduces motion blur by 75% instead of 50%. That special strobe mode on that specific Sony model doesn't need the black frame insertion trick because the TV is doing an excellent job of black frame insertion on a 60Hz signal, if you change the Motionflow setting to "Motionflow Impulse". So MAME doesn't have to. Not all TV's do a good job of 120Hz and 240Hz, and most can't do the trick during Game Mode.
The MAME source code modification only benefits 120 Hz computer monitors that have full control of the 120 Hz signal inside the computer. That's why a source code change is needed. And the modification does it very game-friendly manner, zero added input lag, in a very simple manner. Which makes them great for the amazing LightBoost LCD monitors that came out.