24p questions

[David Lach]

I don't understand what you're saying Thomas. You can't get a "pure" 24p out of 3:2 pulldown. 3:2 pulldown means there is frame alterations because of the way fields are (re) combined that cannot be recovered without recompression.

The Xl2 and DVX100A NTSC do sample 24 (23.976) progressive frames a second, the pulldown is added after to be able to recover the footage in true 24p. That's why you have the 2:3:3:2 pulldown. So you can just discard the extra "fake" frame created by the camera to comply with NTSC 60i. That's also why you can shoot using a 1/48th shutter speed.

So unless I'm not getting your point when you're saying "For NTSC we are fortunate that there is a process to calculate 24p from 30. The camera isn't actually shooting 24p in NTSC. It is shooting 30i that is in a slightly different field format so when we apply a 3:2 pulldown we get a pure 24p" I think this isn't accurate.

[Thomas Smet]

my point is on tape it is 30i. You cannot get 24p onto DV tape without using a different format such as HDV. When you capture your footage it needs the pulldown unless you have a program that captures it as 24P. Yes the chips and shutter speed are at 24 or 48 fps. The raw data is captured at 24p. For NTSC it is then fairly easy to deal with. The camera can then just add a 3:2 pulldown to the 24p raw frames from the ccd and we now have 24p footage that fits inside the NTSC standard. For PAL however what are they supposed to do to get 24P onto a 25P tape? There is no easy formula to do this. The camera cannot do any timeshifts live so this is out of the question.

The fact is that it is much easier to get 24 from 30 then it is to get 24 from 25. A pulldown system cannot be used with PAL video unless you want 20 frames per second video.

30 / 1.25 = 24fps
25 / 1.25 = 20fps *

*if the same 3:2 pulldown system is used.

[Rob Lohman]

The XL2 will indeed sample at 24p and then create 60i/30p from
that. Which is completely reversable without any loss.

In theory the easiest way to do 24p in 25p is simply duplicate
one frame every second. When editing etc. you can simply
remove this duplicate frame. This would be quite easy to
implement on both a camera and an editing application. The
only problems are:

1) there is no standard for this (so no-one supports such a system)

2) I'm not sure who would actually use such system. I doubt there would be enough of these people to warrant a new standard that camera manufacturers and NLE makers will support

[David Lach]

<<<-- 2) I'm not sure who would actually use such system. I doubt there would be enough of these people to warrant a new standard that camera manufacturers and NLE makers will support -->>>

Nobody would use it. The fact remains, even though it can be time consuming because of the software processing involved, converting progressive PAL to NTSC is an easy process. it works with the same 3:2 pulldown principle. Film transfer is even easier. All you need to do is slow it down by 4%. The difference isn't noticeable. Tranfer houses will often do it for you with not additional fee involved.

Every day I wake up wishing we had PAL here in Canada and the US for the higher resolution and closer to film frame rate, but it isn't the case, so we need to live with it. PAL countries are fortunate enough to be able to do everything in 25p. We don't have such an option in NTSC world. Therefore it's important to have a 24p option. It is not important however for PAL camcorders and this is actually the first time I hear someone complaining there isn't a 24p option on a PAL model.

[Rainer Hoffmann]

David,

many people over here in Europe envy you guys in Canada or the US because, so they tell us, you will be having HDTV in a few years. In Europe we hardly know what HDTV means. We will be stuck with PAL for quite some time, it seems. Then again, it means that the XL2 I'm gonna buy in the near future will not be a heap of scrap metal in a matter of 24 month.

[Barry Green]

The XL2 will indeed sample at 24p and then create 60i/30p from that. Which is completely reversable without any loss.

??? Not sure what you mean here by 24P creating 30P. The XL2 CCD's run at three different scanning rates: 24 frames per second, 30 frames per second, and 60 fields per second. Each of those frame rates can get recorded on the 60i tape format and be reconstructed to its original form.

In theory the easiest way to do 24p in 25p is simply duplicate one frame every second. When editing etc. you can simply remove this duplicate frame. This would be quite easy to
implement on both a camera and an editing application.

There are a couple of different approaches to this. Sony, when developing their 24Psf method, apparently just runs the tape a little faster when recording, so they spread 48 fields ("segmented frames," as they call it) across the same tape space that 50i would take up.

In telecine conversions, sometimes they will do what you say, dupllicating a frame, although when going to PAL they will split that frame to make the duplicated frame a little smoother (i.e., one field from the previous frame and one field from the next frame).

But mostly, they do a frame-for-frame transfer, and then just adjust the runtime and the audio to compensate. So 24P gets transferred frame-for-frame to 25P, which means that the program will run about 4% shorter in PAL land, so you have to re-pitch the audio half a semitone lower to keep the same pitch.

Camcorders do exist that do what's being talked about here: 24P/25P/30P/50i/60i, but they aren't cheap... the Sony CineAlta does all those frame rates, but of course it's around $100,000.

[David Lach]

<<<-- Originally posted by Rainer Hoffmann : David,

many people over here in Europe envy you guys in Canada or the US because, so they tell us, you will be having HDTV in a few years. In Europe we hardly know what HDTV means. -->>>

Well I'd definitelly be happier with a 25p/50i higher resolution system here in North America. I guess the grass' always greener on the other side of the fence... ;)

[Rob Lohman]

??? Not sure what you mean here by 24P creating 30P. The XL2 CCD's run at three different scanning rates: 24 frames per second, 30 frames per second, and 60 fields per second. Each of those frame rates can get recorded on the 60i tape format and be reconstructed to its original form.

What I mean is that the 24p signal coming from the CCD's is
pulldown-ed to 60i/30p before it is layed down to tape. Since
the DV spec does NOT allow for 24p to be stored as is on tape.

The NLE (when it supports it) does an inverse pulldown to get
the original 24fps from the 60i/30p footage. This is well known.

The reason I mentioned this (again) was to illustrate that they
are already working around the DV spec and supporting some-
thing like 24p in a PAL camera would require more work arounds.

[Barry Green]

Okay, just making it clear... I've seen many threads where people claim that 24P isn't "really" 24P because it gets converted to 60i, and that's just silly, of course. The cameras DO capture 24 frames per second, and they render motion identically to how a film camera does.

The terminology you used had me confused, when you said that 30P gets created from 24P. 30P is unrelated to 24P of course, and the CCD actually runs at the 30-frame-progressive scan rate to create the 30P sequence.

[Chris Hurd]

Thanks Barry, and let's all please remember that what happens in the camera head is a different thing than what happens in the tape transport. The 24P mode produces the temporal motion of 24 frames per second; maybe the tape transport can't tell the difference but our eyes can. Think of it in the same way as progessive vs. interlace: progressive video is recorded to tape as interlace, except the two separate fields are no longer 1/60th of a second apart (okay, 1/50th for you PAL folks). Does it LOOK like interlace? Heck no, it looks like progessive because that's what it is in the camera head. Just like 24P looks like 24P, because it is 24P, forget about how the tape transport writes it (the only real question is which method you want, 2:3 vs. 2:3:3:2).

[Matthew Cherry]

Hello all,

The XL2 gives you two options for capturing footage at 24p: 2:3 and 2:3:3:2 (I think I typed that right). I'm interested in shooting in 16:9 at 24p and editing in Final Cut HD. I did some test footage at 24p using the default settin of 2:3 and was able to edit it in Final Cut. I subsequently read that the 2:3:3:2 pull down mode was NLE "friendly". I'm not really sure what the difference is or which way I should have the camera set.

Any insight is appreciated.

Matthew

[Bill Ravens]

2;3 is pulldown for ultimate distribution to Video.
2;3:3;2 is pulldown for ultimate transfer to film.

The frame duplication pattern is "undoable in 2:3:3:2, while it is more or less permanent for 2:3. IVTC works on 2:3:3:2.

[Matthew Cherry]

Thank you!

[Raymond Schlogel]

I have yet to experiment but this has been something I've wondered for awhile and more so since getting a camera capable of 24p.

Seems to me if you wanted to slow motion some of your footage that was shot in 24p you would get quite the stagger as there are less frames in the mix. As I understand it in film when planning on doing slow motion they speed up the camera so they have more frames. With this in mind, if you were planning on doing some slow motion would you be better to shoot that in 60p ? In theory this seems to make sense but from what I've seen on television shows that use home movie type footage, when slowed down it still looks like a slowed down camcorder. We know that 60p innately has more of a " camcorder " look than 30 or 24p, but shouldn't it be a close match when slowed or stretched ?

Would love to hear what some of you might know about this.

- Ray

[Yi Fong Yu]

how can one shoot 60p?