Video Asylum

Posted by Joe Murphy Jr (A) on May 15, 2007 at 22:30:25

In Reply to: 1080/24p vs 1080/60p - Vertical Res still not clear... posted by blackpixels on May 15, 2007 at 11:39:16:

1080p24 is what's recorded on the disc (for films). Getting this native rate signal out of the player, for displays that are capable of accepting it, is the best way to do it. The display can then refresh at 48Hz or 72Hz and give you the best progressive picture possible from your player/display combination. Unfortunately, there are two current problems with 1080p24: there are few displays at this time which accept this rate and some of the ones that do will change the rate back to 60Hz because that's the native rate of the display. Neither problem is a reason to exclude this output as an option, because more displays in the future will accept 24p and a higher percentage of those displays will properly refresh at a multiple of 24 (48, 72, etc).

And what about 60p? The encoding on the disc is obviously not 60p. To create this rate, the player will actually output each successive original frame either 3x or 2x in order to get the rate from 24 to 60 (Frame 1 = 3x, Frame 2 = 2x, Frame 3 = 3x, Frame 4 = 2x, etc giving the appearance of 60 frames instead of 24). As you can see, Frame 1 appears for 3/60 sec, Frame 2 appears for 2/60 sec, Frame 3 appears for 3/60 sec, Frame 4 appears for 2/60 sec, etc and this can introduce an artifact called "judder" (a "jerkiness" in the on-screen motion caused by each successive original frame appearing for a different length of time). Some people are sensitive to this artifact, some people will only notice it if it's pointed out to them and others don't notice it at all. Outputting a 24p signal and letting the display refresh it at a multiple of 24 (48, 72, etc) eliminates this problem.

Click the link below and scroll down a bit to see some animation as to how this process works:

• 24 to 60   (Open in New Window)