refresh rate matching

[mindbomb]

A lot of software has this feature to change the display's refresh rate to match the video's frame rate, but I am wondering why it is supposed to makes things smoother.

Shouldn't you be fine as long as the refresh rate is greater than or equal to the video's frame rate?

Also, does this apply only to TV's with hdmi?
I don't seem to notice any problems with smoothness using dvi or analog without the refresh rate being matched.

[Šabović Adis]

I guess it's because:

-to match=to compute (more)
(extra computation not needed if video&refresh rates are equal)

Thanks, Šabović Adis

[Asmodian]

The two reasons I want the refresh rate to match video frame rate:

1) Tearing: If you are half way though displaying a frame (on the screen) when the decoder gives you the next frame you get a horizontal line where the image changes. The top of the screen is one video frame while the bottom is the next. V-sync keeps this from happening.

2) Judder: With V-sync on you only display a new frame when you have completely displayed the previous frame. This results in no tearing but if the refresh rate doesn't match you end up displaying, for example, one frame for two monitor refreshes and then the next frame for three, a 50% longer display time for some frames vs others. This gives a subtle (to some, I notice it right away now) judder most noticeable during pans etc.

If you don't notice any of these issues DO NOT train yourself to notice them. Now I hate most computer video playback (YouTube, Hulu, Netflix, etc.). :p

This applies to any connection.

[hello_hello]

A lot of software has this feature to change the display's refresh rate to match the video's frame rate, but I am wondering why it is supposed to makes things smoother.

Shouldn't you be fine as long as the refresh rate is greater than or equal to the video's frame rate?

Ideally the refresh rate should be an exact multiple of the frame rate. ie 25fps/50Hz, 30fps/60Hz etc. That way there's 2 refreshes for each frame rather than having to occasionally repeat frames more than twice etc which can cause "judder" in motion.

24fps is a problem because traditionally it's 50Hz for PAL or 60Hz for NTSC, which is why some TVs can use higher refresh rates if they have a "film" mode. Judder has always been a problem for NTSC.
My TV doesn't have a film mode, but fortunately as I live in PAL-land I can use Reclock to speed 24fps video up to 25fps which effectively gives me a PAL "film mode", so I just watch everything that way.
Unfortunately my Bluray player isn't very clever. When using the USB input to play video it connects at 60Hz regardless of the frame rate (it'll change refresh rates for discs), which is one of the reasons I use a PC for playing video.

Also, does this apply only to TV's with hdmi?
I don't seem to notice any problems with smoothness using dvi or analog without the refresh rate being matched.

Yes it applies to HDMI/DVI. If you're not seeing any smoothness problems it's probably a good thing. Once you start looking....

My TV only lets me connect at 60Hz when using VGA, but some TVs probably let you use other refresh rates. When connected via HDMI/DVI (or VGA) the video card should list the refresh rates supported by the TV. If you're in NTSC-land 60Hz may be the only choice.