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Verifying my knowledge on pulldown


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#1 David Calson

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Posted 14 March 2009 - 12:26 PM

Okay so I already did a search but don't think the answer is around here yet,

So a camera that shoots 24p with pulldown puts the 24 or 23.978 frames into a NTSC 29.97 friendly wrapper right? This is so it plays friendly with NTSC systems and what not, but don't dvd players and tv's automatically add this pulldown anyways? If so, why is the camera 'helping' me?

Also, if the 24p footage is pulled down to 29.97 frames, why does it still look so film-like?

So I think I heard that the only difference between watching true 24p footage and 24 pulled down footage is that the pulled down footage has a more slight blur to it right?

Another thing I hear is, you gotta pulldown if you're putting that on the web, at least I thought I heard that, if so why? Okay thanks for your responses.
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#2 Del Collens

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Posted 17 March 2009 - 01:20 AM

Well, I'm an editor so I think I can possibly help you with this.

Good video camera example is the Canon XL2, it shoots miniDV Standard Def at various frame rates, all within either 1.33:1 or 1.85:1 (which, depending on the camera you're using, is 4:3 & 16:9 non-anamorphic).
It can shoot the following frame rates;
60i (59.94fps)
30i (29.97fps)
24p (29.97fps - emulated 23.98)

Now what the camera is doing 'in-cam' is a 3:2 pulldown, meaning that it's actually taking quarters of a frame every 3/5 frames in the TC and counting it as a whole, and rounding it off, dropping it on 6 black frames, plus more mathematics, etc, etc. This is why you're getting the 'blur' type 23.98 effect.
The reason for this is primarily the 'film look' and broadcast standards regarding 29.97.
Almost 99% of the news you see is shot 30/60 drop-frame on digibeta.

I haven't seen a 'true' 24p video camera that isn't emulating 23.98 that's SD.
Most SD cameras and footage I've worked with that is claimed to be 23.98 is actually 29.97 with the pulldown.

Film has no p/i, it's film and the camera framerate is 24 (23.98).
HDV is emulated all over the place and compressed in-cam heavily.
HD, depending on the camera is capable of many framerates/resolutions, and is compressed using a Hard Codec in camera to either a tape or drive.
SD is capable of 29.97, emulated 23.98, and higher, recorded to smaller tape and often not compressed in camera.

There are many rogue formats, which is often why people have problems with Avid supporting only industry standard formats, but that's another story. A good example of a rogue format is the Canon XHA1, which is HDV, shoots up to 1080i at a emulated 23.98 called 24F, but is a pulldown to 29.97, image flipped, and compressed in-cam as a MPEG-2 stream, to a miniDV tape. An editors worst nightmare.

Depending on who authored the dvd or what format the film was mastered, the framerate on your dvd player is usually 1:1. Meaning if it was shot on film at 23.98, mastered at 23.98, authored at 23.98, you're watching it 23.98.
I've never seen a dvd player doing a pullup or pulldown, if your dvd player supports the formats along with your screen/projector,etc you'll get the authored framerate.
If you shoot at a emulated 23.98 that is really 29.97, don't author it 23.98. It's the difference between two completely separate pieces of equipment and a DVD player is not going to reverse the in-cam process, if you can even get it past the mpeg2 encoding.
I've seen this before and the image is a skipping mess.

Most poop on the web is VBR and compressed heavily using a codec of their choosing. As long as the viewer has the codec you used to compress the video it's going to be viewable.

Hope that answered a couple of your questions.
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#3 Kevin Mastman

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Posted 17 March 2009 - 10:03 AM

Hi Del,

I'm glad this topic came up because I'm confused as well. I've been looking at the Sony Z7U which as I understand is the first HDV camera to shoot true 24p. What are the advantages/ disadvantages of shooting 24p if the footage is going to be used on an sd dvd? Am I going to run into trouble pulling it to 29.97 quality wise, or do I even need to do this? Can it stay in 24p for the round trip through editing and on the DVD?

Thanks,

Kevin Mastman
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#4 David Mullen ASC

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Posted 17 March 2009 - 12:13 PM

23.98P / 24P mimics the look of 24 fps film by capturing a whole frame 24 times a second.

Like with 24 fps film, when this is shown on a 60i (59.94i) monitor, it needs a 3:2 pulldown to convert 23.98 to 59.94.

A DVD can store progressive scan 480P/23.98 and the player will add the 3:2 pulldown on playback for an interlaced-scan monitor.

The main issue you have to deal with is whether to cut in true 24P or cut footage with a pulldown -- if the 24P capture was recorded to 60i with a pulldown, you may want to remove the pulldown before editing if you want to create a 24P master. Otherwise you could cut this as a 60i project but then the pulldown cadence will be broken up.

The other advantage of having a 24P master is that it may be easier to convert to 50i PAL than 60i footage with a 3:2 pulldown would be.
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#5 Del Collens

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Posted 22 March 2009 - 11:11 PM

Hi Del,

I'm glad this topic came up because I'm confused as well. I've been looking at the Sony Z7U which as I understand is the first HDV camera to shoot true 24p.

What are the advantages/ disadvantages of shooting 24p if the footage is going to be used on an sd dvd? Am I going to run into trouble pulling it to 29.97 quality wise, or do I even need to do this? Can it stay in 24p for the round trip through editing and on the DVD?

Thanks,

Kevin Mastman

Look of the picture.

I'm ignorant when it comes to all the details of many of the cameras being released, so I couldn't tell you if it's actual 23.98 that the Sony Z7U shoots. A good bet would to be to find out what codec it uses, this will tell you a lot.
For instance, the hvx-200 is DVCPro HD, and that codec is capable of doing true 23.98 without a pulldown, granted it doesn't appear to have the same picture quality (talking pixels) as the Sony HDW-f900, but DVCPro HD meets industry broadcast standards and then some. It's highly possible that camera does this as well, but you never know.

So in my opinion, if you're going to be the one editing it and mastering the cut and Authoring the DVD - Test it.

Depending what you're going for, as with most companies, they have a workflow and usually the authorers make the DVD as compatible with all systems as possible. To prevent conflicts with dvd players, most houses that I know author all the footage regardless if it's progressive as interlaced, saving progressive for HD DVDs.
As you might already know, if you play a progressive compressed MPEG2 converted dvd in a non-progressive dvd player, it will either not display, or you'll get pixilation, skipping, etc.

So one instance of a test was;

Shoot anything for 5 minutes. Use every frame rate and resolution your camera supports for these clips, and then bring them into your editing system using the different quality codec's provided (in Avid/FCP/Premiere,etc).
Most formats have a standard, which are virtually 1:1 of the original master footage, you'll find it for your camera.
(For instance in Avid, the standard codec for miniDV or DVCam footage is dv 25 411)

Now once you're done testing that, make some exports of your clips, then in a 3rd party app such as Sorenson Squeeze, make some MPEG2's with various settings and burn them to dvds, drop them in your player to test and there you have it.

HDV is a tough call and can give you more headaches than necessary. But just remember you can always convert virtually any format to one compatible for playback. But if quality is a big concern, as it should be, I would definitely do some research as to the workflow for an HDV camera. Highly possible the end result will be something you do not want.
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#6 David Ghast

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Posted 23 March 2009 - 01:11 AM

Theres no reason to become obsessed or confused with all this information, although it is important to understand. A general rule of thumb is:

1. If you can record in progressive, do it, and keep it progressive. If you plan on doing any rotoscoping or local effects, you'll understand why.
2. If you record in interlaced, dont deinterlace it unless your doing rotoscoping.
3. Deinterlacing is a very lossy process, interlacing is not.

And for the love of god, dont let telecine con you into doing a hard pulldown on your film material (which will interlace it), you can easily do this in post, even though theres no reason to.
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