Why PAL & NTSC files works directly

[Limoscha]

Just wondering, why video files .avi or .mkv play correctly on every computer.

My computer is PAL 50 Hz (25 fps) but it still can play content fine of NTSC 60 Hz (23.975 fps).

In VHS era, you have to convert NTSC tapes to PAL somehow before you can watch them, and picture quality was usually bad.

So why it works directly?


BTW, It seems that all? LCD monitors/televisions has 60 Hz at use, even if my electrical socket gives out 50 Hz.


Why it is so?

But :thanks:for anwers anyways

[vivan]

Because PC is smart.
It can show content of any fps on any display. E.g. 24 fps on 60 Hz screen looks like that: first frame is shown for 2/60 s; second - 3/60 s; third - 2/60 s; fourth - 3/60 s and so on. Since frames has different duration video wouldn't be as smooth as it could be if video fps was multiple of display freq (like 30 fps on 60 Hz display, or both 24 and 30 fps on 120Hz), but it still looks ok.
Also you can change video fps on-the-fly using reclock.

And PC can't be PAL.

[AnonCrow]

My computer is PAL 50 Hz Would that be an (classic) Amiga or an Atari (Falcon) ?

In both cases you probably wouldn't be using the native video output (and chips) anyway, but would have installed a 3rd party video card after having installed a PCI expansion slot.

[Vurbal]

Just wondering, why video files .avi or .mkv play correctly on every computer.

My computer is PAL 50 Hz (25 fps) but it still can play content fine of NTSC 60 Hz (23.975 fps).

In VHS era, you have to convert NTSC tapes to PAL somehow before you can watch them, and picture quality was usually bad.

So why it works directly?


BTW, It seems that all? LCD monitors/televisions has 60 Hz at use, even if my electrical socket gives out 50 Hz.


Why it is so?

But :thanks:for anwers anyways

What makes you think your computer uses PAL? Those are broadcasting standards which have no relevance to any modern computer outside of connecting it to a (SD) TV.

[petran79]

only if his VGA card has analog video out and he is connecting it to a TV. But picture would look horrible

[shimaflarex]

Your PSU converts the 50hz electrical AC to DC.
All your computer components works on DC, the original AC frequency isn't relevant at all.

As for how you can play movies perfectly on a 60Hz display, well, as vivan said, it is done by duplicating frames.
You end up getting a slightly jerky movie, but it is mostly unnoticeable (unless you know about the problem and is looking for it :).
You can avoid that if you match the monitor frequency to a multiple of the movie's FPS.