- [Instructor] There are three factors that can affect
the display of the refresh rate for video on a monitor,
or for that matter, on a projector:
the frames per second of the video,
the refresh rate of the screen,
and the refresh rate of the lamp in the screen.
Let's start backwards.
The refresh rate of the lamp is usually much higher
than the refresh rate of the screen.
Let's say typically 200 Hertz, that's 200 times per second.
By the way, I love explaining what Hertz means.
There was a time when we didn't have a word
for things that happened repeatedly every second,
or times per second.
A German fellow called Heinrich Rudolph Hertz
proved the Theory of Electromagnetic Waves
in the late 19th century,
and cycles per second were named in his honor.
So Hertz just means times per second, or cycles per second.
If the lamp in a TV or projector runs at 200 Hertz,
it's easily faster than the refresh rate of the screen.
Screen refresh rates are usually set
as the same as the video standard display.
So that's 60 Hertz for NTSC, and 50 Hertz for PAL.
Screens often boast faster refresh rates,
which are useful for faster frame rate content
like some video games,
but won't do all that much for regular media.
In fact, if your TV runs at 120 Hertz,
which is a common refresh rate
marketed as an improvement in picture quality,
the system will just repeat every frame twice,
or every every field four times,
redrawing the image each time the screen refreshes.
This higher responsiveness in the screen
will make a marginal difference to improve the picture,
but in many cases, it'll make it worse
because of the way the TV manages the signal.
You might find you get a better image
by setting the TV to match the frame rate
or field rate of your footage,
which brings us to the frames per second.
If you're producing NTSC, it'll be 29.97 frames per second,
and if it's PAL, it'll be 25.
If your media matches the common frame rate
of 24 frames per second used in film,
it'll make little difference
if you're in an NTSC or PAL territory.
In any case, you'll probably find you get the best results
by matching your screen refresh rate
to your media frame rate.
Occasionally, major feature films have been screened
at double the normal frame rate,
that's 48 frames per second.
Though this actually improves
the appearance of movement and the clarity of the image,
at least in terms of your brain's perception of the image,
some audience members complain this looks too smooth,
and therefore, too much like video.
Improving the appearance of movement
was part of the reason fields were used in video.
And we tend to see the lesser quality
of 24 frames per second used in film as an improvement,
because we relate to it as being more film make.