Telecining film: 24fps -> 29.970 or 24fps->59.94?

[Farfel]

I've been reading up on HD specs, and have learned about all the processes in place to manipulate video sources to display according to the given standards. I just now realized that 720p is capable of displaying 60fps. Prior to this, I assumed all film and video sources were captured at 24fps and 30fps, respectively. I had no idea 60fps was actually being used, which explains why the "720p is better for sports" claim actually hits home now (More frames to display fast motion in the same chunk of time).

At any rate, my question is more general about the telecine process. Is film source at 23.976fps converted to 29.970fps or 59.94fps via the 3:2 pulldown procedure? It seems to me that it would be the latter, as the 3:2 pulldown procedure alternates between doubling and tripling frames to achieve the desired fps corresponding with American TVs' 60hz refresh rate. But if that's the case, how is this statement from this Wikipedia article (http://en.wikipedia.org/wiki/Telecine#3:2_pulldown) accurate:

The process of converting 24 frame/s material to 29.97 frame/s is known as 3:2 pulldown

Further, how is 720p24 material converted to 720p@60? It can't use the same process as above, can it? It needs to achieve 60 frames per second, not fields. Surely it must somehow get converted to 29.970fps and then have each of its frames doubled to achieve 59.94 right? I'm a bit confused :)

[Guest]

The MPEG2 spec allows for field repeats or frame repeats. For 23.976->29.97, you use field repeats like this (top fields on the first line, bottom on the second):

a a b c d
a b c c d

Four frames have become 5 by repeating two of the fields (a and c).

For 23.976->59.94, you use frame repeats:

a a b b b c c d d d
a a b b b c c d d d

Four frames have become 10 by using repeat-by-2 and repeat-by-3 flags.

[Farfel]

So basically in order for 720p24 to become 720p60 the source's frames get either doubled or tripled?

ABCD becomes AABBBCCDDD from how I understand your post.

So my next question is why isn't this evident when you watch the video itself? I mean, every other set of frames being tripled (compared to the other set being doubled) would seem to be quite noticable, no?

Also, if capturing a 720p source, such as ABC or Fox, how does one determine if the original source is 720p24, 720p30, or real 720p60 (60 unique frames per second)?

Thanks!

[Guest]

I mean, every other set of frames being tripled (compared to the other set being doubled) would seem to be quite noticable, no? No.

Also, if capturing a 720p source, such as ABC or Fox, how does one determine if the original source is 720p24, 720p30, or real 720p60 (60 unique frames per second)? You just step through the frames and identify the duplicate patterns.

[phædrus]

Is there any real 720p60 being broadcast in the US? In my town in the midwest, we have 6 HD channels, and 2 of them are 720p. But I have not recorded anything that was 60 progressive fps. Does such an animal exist? It seems it would put a strain on quality, given the bitrate.

[wonkey_monkey]

I mean, every other set of frames being tripled (compared to the other set being doubled) would seem to be quite noticable, no?

No.

Or, to offer another opinion, yes? ;) If you compare native 30p (doubled to 60p) and 24p 2:3'd to 60p, the former is (to me) noticeably smoother than the latter.

That said, people in NTSC-land are used to viewing things this way, just as I'm used to viewing them with the 4% chipmunk factor.

David

[Guest]

The OP said "quite noticable". If it were, every Joe Six Pack would be complaining, but I hever heard any average Joe mention anything.