fps basics

[saprano]

Originally Posted by saprano

Can somebody explain to me what pulldown does and how it works.

For starters, let's explain why the 3:2 pulldown process is necessary. If you have ever seen a reel of film, you know that it is nothing more than a bunch of still pictures run at a rapid rate in order to create the appearance of fluid motion. In the movie theater, each second of film is actually 24 of those still pictures (or frames).


While film runs at 24 frames per second (fps), NTSC television signals (or video) have a run rate of 30 fps. In fact, television is also different from film in another significant way. Film projectors project the entire image all at once. TV's actually draw (or burn) each of the 525 lines of resolution on the phosphorus gray material on the front of your television. However, they cannot draw all 525 lines at once without noticeable 'flicker.' A system was created that eliminates flicker by drawing only half of the 525 lines per half second. Odd lines (lines 1-525) are drawn first in one 'field,' followed by the even lines (lines 2-524) in a second 'field.' So, you have 30 frames per second, or 60 fields per second. This system is called interlacing.

If you have paid attention so far, you might start seeing a problem. First of all there are 24 fps in film versus 30 fps in video. Secondly, video has two fields per frame whereas film does not have fields at all. That means we cannot simply transfer the film to video without issues. If we simply showed 24 fps on an NTSC display, what we would see is jerky, sped up action, much like an old "Keystone Cops" movie.

This is not a new problem, since we have been converting film to video for years. We even have a name for the process. It is called 'telecine' or 3:2 pulldown.

[davidpet]

Why/how are tv shows that are listed as being recorded in 1080i60 on the web being released on blu-ray at 1080p24? Are they downgrading from 30 fps to 24 fps just to get a p on the box, or are they actually being recorded in 24 fps and the websites that list them as 1080i are wrong? The shows I'm talk about include Supernatural and Smallville.

Also, as a side note, how come I can't start a new thread (which is why I had to post this question in an old thread and hope that someone reads it)?

[Steve]

Originally Posted by davidpet

Why/how are tv shows that are listed as being recorded in 1080i60 on the web being released on blu-ray at 1080p24? Are they downgrading from 30 fps to 24 fps just to get a p on the box, or are they actually being recorded in 24 fps and the websites that list them as 1080i are wrong? The shows I'm talk about include Supernatural and Smallville.

Also, as a side note, how come I can't start a new thread (which is why I had to post this question in an old thread and hope that someone reads it)?

I'll let someone more knowledgeable in film and video conversion answer your first question.

With regard to your second question, you can't create a new thread of your own until you've made a minimum number of posts, and so far you haven't met that minimum. I don't remember what the number is, but I'm pretty sure it's only like 10 or less.

Oh, and by the way, welcome to the forum.

[crazyBLUE]

If I'm not mistaken , It is recorded at 24 fps .

[Coolpplse]

Originally Posted by davidpet

Why/how are tv shows that are listed as being recorded in 1080i60 on the web being released on blu-ray at 1080p24? Are they downgrading from 30 fps to 24 fps just to get a p on the box, or are they actually being recorded in 24 fps and the websites that list them as 1080i are wrong? The shows I'm talk about include Supernatural and Smallville.

Also, as a side note, how come I can't start a new thread (which is why I had to post this question in an old thread and hope that someone reads it)?

Most nowadays are being shot at 1080p24, the reason why you see 1080i 60 caps on the web is because US HD Broadcast networks either stick with 720p or 1080i 60, so when 24fps shows are being played, a 3:2 pulldown flag is applied to the stream making it repeat frames to 60...

[saprano]

Why did i quote myself? I don't remember doing that.