24PA and tape dubs

j-beat · January 12, 2004

I need to dub some tapes I shot on a DVX-100 in 24P Advanced. I also need to put NEW timecode into these tapes. Does anyone know if the dubbing of tapes with new timecome in any effects the 24PA pulldown?

thanks for any help

Mitch Gross · January 12, 2004

You'll lose the flagging on the frames that makes extraction of the 24p simple. If you are watching in standard 60i this makes no difference, and if you do later need to extract the 24p then you'll have to hunt a little but it's not impossible (there are only five choices).

j-beat · January 12, 2004

thanks mitch.

I've been told if I dub via firewire I won't use the flags so is it because of the new timecode that I'll lose the flags? And if so -- it seemed from your message that there was still some way to read the flags and extract the pulldown? That so? And how is that done? I'm capturing the footage on a MAC using FCP4

josh

Mitch Gross · January 12, 2004

The flags are embedded in the user bits of the timecode, so if you generate new timecode then you lose the flags. However, there is a fairly simple order to the flagging (24p = 2:3:2:3:2:3, 24pa = 2:2:3:3:2:2:3:3), so it can be fairly easy to figure out what the extraction needs to be. You simply need to know whether you're in 24p or 24pa and pick the correct starting field, a one out of five shot. I believe 2-pop has a more in-depth discussion on this and how to deal with it. Frankly, since you're using FCP4 you should have absolutely no problem--Panasonic and Apple worked together to develop a system that would make their products work swimmingly together.

j-beat · January 12, 2004

Thanks mitch --

I get you up to a point -- I'm just not exactly sure what you mean when you talk about the "correct starting field". How can I determine that? I've been capturing everything so far (non-dubbed tapes in 24PA) in 29.97fps with the 2:3:3:2 advanced pulldown.

thanks again for your help on this.

Mitch Gross · January 13, 2004

The 24p frames are spread across 60i fields. A 24p frame is made up of two fields that are captured by the sensor at the same time. The order of the spread is what is indicated by the 2:3:3:2, meaning it's 2 fields of frame 1 of 24p onto two fields of 60i, then 3 fields of 24p onto 3 fields of 601, and so on. So you need to know where that sequence starts on the 60i material in order to reconstruct the original 24p. The flags will tell you, but otherwise you can simply guess until you find the right one as there are only five possibilities until the sequence repeats itself.

If this is not clear, try this. Get yourself a set of checkers, red and black and label them A & B. Line them up in a row as red A, red B, black A, black B, black A, red A, red B, etc. In order to reconstruct the 24p signal, you need to stack red A & red B then black A & black B. It's easy to do when you can see the colors--just drop the 5th field and combine the others. That's if the frames are flagged. But if they're not you are essentially doing it with your eyes closed. There are five possible choices for a start point, after which the sequence repeats. So you can try it blindly and if you're wrong you just move on to the next one until you get it right.

BTW, how you do this in your editing program I have no idea. Ask someone familiar with FCP4. This is possibly the single most confused concept in the DV world today. You don't know how many people cannot wrap their heads around 24p on 60i.

j-beat · January 13, 2004

Mitch thanks for helping me out with this ---

I more or less get the principle of the pulldown (how the frames are arranged to conform to the interlacing of video) but what I don?t understand is how to SEE the 24PA ? i.e. how to know if it?s there by watching the footage. I get your analogy of the checkers but how does that apply to the footage? When I go frame by frame through what I shot I do not see any interlacing or difference between frames. Is there some way I should be able to see the pulldown or flags?

Thanks again for your patience

josh

Federico Pedroza · January 13, 2004

Hi

First of all what is the visual difference between 24P and 24PA? does one look smoother or more film like than the other?

Second, If I shoot on either, will I have any problems while editing on Premier? and what should I avoid in order to be flag problem free.

Fred

Alvin Pingol · January 14, 2004

First of all what is the visual difference between 24P and 24PA? does one look smoother or more film like than the other?

Yes. 24P is both smoother and looks more "film-like" than 24PA, as the pulldown pattern used, 3:2:3:2, is the same as 24fps film material (e.g. motion pictures) transferred to video.

Mitch Gross · January 14, 2004

I more or less get the principle of the pulldown (how the frames are arranged to conform to the interlacing of video) but what I don?t understand is how to SEE the 24PA ? i.e. how to know if it?s there by watching the footage.

You're watching 60i unless you choose to transform it into 24p. When you choose to do so you'll certainly know if you got the sequencing correct. It's ether perfect or a real mess, with fields from separate frames mixed together to make a hodgepodged image.