24p Vs 25p, an interesting thought.

farss wrote on 5/26/2006, 5:23 PM
Certainly no one can see the difference between film run at 24fps or 25fps but that's not what this is about rather it's about how it gets processed in post. And I have to thank Grazie and his Glow problem for the spark that lit the fire in my brain here.

25p pretty well always ends up in video as 25PsF. One can very simply merge the fields to get back the original frame.

24p ends up as 24PsF with two possible variants defining how the pulldown is applied. A simple field merge will not produce the original frames for every frame, to get them back some intelligence is needed and only for 24pA is it 100% accurate.

So what?

Well it doesn't mean much until you start applying FXs. As Grazies problem highlights merging interlaced fields to add FXs can get things screwed up introducing flicker. Yes, interlaced video is a PIA.

But before the progressive scan mob get all uppity consider this. As i noted above 25p will always field merge to produce a correct frame, the fields will truly have no temporal separation. One for the PAL mob I guess.

Now for 24p if we do a IVTC so we're apply FXs to the original frames then again all is sweet. But what if we didn't. We've now got an interesting set of problems. For certain frames in the sequences with an FX that relies upon merging fields we're inevitably going to introduce flicker or judder on moving objects!

Why does any of this matter. We'll I've read a number of posts (mostly elsewhere and I suspect they're not Vegas users) from people saying they're abandoning 24p as it's just too jerky, has too much flicker. Now I found that odd, properly shot telecined film always looks fine to me and some of these posts were from guys that had plenty of film experience.

So my gut feeling is there's nothing wrong with their 24p footage, it's how it's being processed in post. Now I don't know much about how any other NLEs apart from Vegas process 24p. I know that with care (removing pulldown) in Vegas one could avoid these problems. Certainly food for thought on a cold Saturday morning.

And then again I could be totally way off beam....

Bob.

Comments

Spot|DSE wrote on 5/26/2006, 5:30 PM
So my gut feeling is there's nothing wrong with their 24p footage, it's how it's being processed in post.

I'm sonvinced this is virtually always the case. This is why you should be using a 23.976 timeline in Vegas for anything that is going to that framerate, so that transitions, temporal filters, etc are always in the correct mode. Trying to apply transitions after the fact can create some seriously funky footage.
David Jimerson wrote on 5/26/2006, 6:30 PM
In my experience, those who who want to "give up" on 24p footage are chiefly those who never learned how to shoot it properly.

And that's partially understandble; most came from the 60i world where any which camera move ends up fine and there's no strobe or stutter, and there's a dearth of material out there explaining how to shoot good 24p.

But it's really all in how it's shot. If you shoot it properly, and choose the correct pulldown scheme for the purposes of what kind of timeline you're going to edit on, you won't have the problems often complained about. You won't have the stutter, except that which is appropriate to give it a film-like cadence.

It also doesn't help that aside from having such a limited amount of material out there, there's also a whole lot of bad information and persistent myths about pulldown, etc., so people get bad instruction which results in bad footage, and then it's even compounded by not matching your pulldown to your intended purpose.

(And, by not using Vegas to cut it! Too many other NLEs make itway too complicated -- and yes, I'm looking at you, FCP -- and it just makes things that much worse.)

For example, there should be no problem cutting 24p standard in 60i. But cutting 24pA in 60i can result in the problems complained about. But people hear that only 24pA is "true" 24p, so they shoot in 24pA to cut in 60i instead of shooting in standard 24p, which is what they should use, but they think it isn't "true" 24p. And because of the arrangement of frames in 24pA, the footage stutters.


farss wrote on 5/26/2006, 6:57 PM
Well from what I'm postulating you should NEVER cut 24p as 60i.
The ONLY correct way to do it is to remove the pulldown and edit / add FXs to the native frames.
The reason why 24pA is better is because there's no way to extract the original 24 frames from 24p. As to which looks best at 60i I haven't a clue and isn't really relevant to this issue.

Bob.
Spot|DSE wrote on 5/26/2006, 7:05 PM
In my experience, those who who want to "give up" on 24p footage are chiefly those who never learned how to shoot it properly.

Spend some time on the various DP forums out there, and see how many Hollywood guys want to get away from 24p, folks on the CML lists, etc. You'll be surprised at how many that make their living shooting 24p don't want to shoot it unless they have to. For them, it's not a romance with film "look" but rather a necessity to match to film that is being shot at the same time. In the case of the King Kong BTS, they experimented with both 24p and CF25, and ended up liking the CF30 better, and ended up choosing Z1's for that specific reason.

24p is a tool. It's a grossly over-exaggerated, marketed, and hyped too, moreso than anything in the history of video, but still just a tool for a specific look. We shoot 24p when the client wants it. New clients are always asked (when they request 24p) "Why?" If their response is that someone who they know told them it needs to be 24p, we show them a short vid of the same motion in 24p, 25p, 30p, 50i, and 60i. Most of the time, they choose either 30p or 60i when offered the choice. They're viewing on a projector, so they're seeing it large, closeup, etc.

For some projects, 24p is a necessity. For others, it's an absolute "don't go there." It's not the be-all, end-all that some folks have bought into.
but back to topic, much of the 24p media out there is improperly processed. Spend some time working with other apps, and you'll immediately understand what Farss is referring to. Vegas is a luxury for 24p editors, but even Vegas can screw it up if it's not understood.
BarryGreen wrote on 5/26/2006, 7:05 PM
>>because there's no way to extract the original 24 frames from 24p<<

Sure there is; Vegas will do this automatically on the fly in fact. It's cleaner to do it from 24pA, but it's perfectly possible to do it on normal 24p (or, on film footage that was transferred to video using 2:3 pulldown too).

But yes, I do totally agree that you would get better results from editing on the 24p timeline and do your graphics/titles/etc. in 24p, and if needing to go back out to 60i, do that as a last step. I think you're completely correct in that assessment.
David Jimerson wrote on 5/26/2006, 7:25 PM
I think you might have missed my point a little bit, Spot.

I'm not saying that 24p is the best format, etc; of course it's a tool and every tool has its proper use. I like it; doesn't mean everyone does or should and I'd never presume to say they should.

I'm just saying that for the reasons many people give up on it, as stated in this thread -- stutter, stutter, stutter, i.e., perceived problems with the look of it, not frame-matching, timecode issues, sound sync, etc. -- most of it comes from it being used improperly.

'sall I'm sayin'.
farss wrote on 5/26/2006, 7:39 PM
I think there's a much wider problem overall.
Today one person can do what used to be done 100s split over many departments and it's affordable enough for just about anyone to have a go.
Problem is those 100s of people had a vast wealth of knowledge, some had great creative skills and others great technical skill, either way they spent lifetimes honing their art or their science.

Trying to roll all of that into one brain is a pretty big ask.

Another thing that never ceases to amaze me is the number of people who'll roll hours of tape (or film) and THEN worry about how they're going to post it. Last year I was asked to help resolve a really sorry mess. This crew shot half the production at 24p and the rest at 25p, I ran, very fast. I'm not talking a tin pot mob either, they had very serious budgets.

Today I'm doing a trivial corporate job. But for some reason they shot most of it 4:3 and some at 16:9!
Coursedesign wrote on 5/26/2006, 8:17 PM
25p pretty well always ends up in video as 25PsF. One can very simply merge the fields to get back the original frame... 25p will always field merge to produce a correct frame, the fields will truly have no temporal separation. One for the PAL mob I guess.

25p, yes.

50i PAL? No.

If you shoot a moving car say, with a locked down camera at 50i, then merge the fields, you'll get some naahhsty jaggies because the fields don't match.

In practice it takes some manual work to get the best deinterlacing, preferably with more advanced tools than what Vegas provides.

ReelSmart FieldsKit is one relatively inexpensive AE plug-in for this that has more controls for this, and Magic Bullet Suite is decent too if you dig into it.

Same thing with frame rate conversion: Twixtor and other specialized tools (including Magic Bullet Suite) can generate very nice looking new intermediate frames from "thin air" so to speak, better than what Vegas can do on its own.

Does anybody know if CMOS sensors have the same problems when shooting native progressive as CCDs do? Less sensitivity, etc.

It would seem that all the CCD issues are unique to the type of charge brigade that carries the light signal (Charge of the Light Brigade? :O).