Clarification of "24fps progressive-scan DV"

Infinite5ths wrote on 12/29/2005, 11:53 AM
OK folks....I've been reading the Vegas 6 & DVD Arch 3 manuals, and I'm a bit confused by one phrase of their terminology.

I understand 2:3 pulldown, why it's used, how it's implemented, etc. What I don't understand is the option in Vegas & DVD Arch to "Allow pulldown removal when opening 24p DV".

If I understand correctly, a true 24p file/tape DOES NOT CONTAIN pulldown. Pulldown is only added when transferring/saving to 29.97fps (fps=frames per second) interlaced video (commonly called "60i"). WHY then would one need to remove pulldown from a 24p DV file??

The only way I can resolve this is as follows: Perhaps it is not actually possible to create/save true 24p video (24 full frames - NOT FIELDS - per second) in a DV file or on a miniDV tape. In that case, what Sony's manuals have called a "24fps progressive scan DV video file" is actually 29.97fps (60i) DV - which is (of course) created by splitting 24p into FIELDS & adding pulldown. (In other words, the file is not really 24p at all). In that case, it would be necessary to REMOVE the pulldown (and recombine the fields into frames) to get back to true 24p video in Vegas, etc.

Am I on the right track here?
--
Mike

Comments

Coursedesign wrote on 12/29/2005, 12:03 PM
Yes.

Perhaps to allow playback on a directly connected TV.
Infinite5ths wrote on 12/29/2005, 12:09 PM
OK. Thank you.

I'm not quite sure what you meant by the "directly connected TV" statement...

Are you suggesting that pulldown removal would avoid adding pulldown to the same video twice (one when recorded, once when output for preview) when feeding an external TV from Vegas or DVD Arch?
--
Mike
farss wrote on 12/29/2005, 12:56 PM
One removes the pulldown so that the FXs are rendered at 24p also. This is optional, you may prefer to have your FXs rendered at 60i, lots of US sitcoms seem to be done this way, shot on film, transfered to video with pulldown and edited as vanilla 60i NTSC, the 'look' I'm told is slightly less filmic, only during the FXs I'd guess.
When you're editing a 24p project then pulldown I think would have to be added for external preview devices unless you were using one capable of handling 24p. Bear in mind that 24p display devices also actually run at 48Hz, even film projectors (two blade shutter), otherwise flicker.
The best reason for doing a full 24p project is for DVD or film out, the DVD spec supports encoding just those 24 frames, on playback the player adds pulldown. This avoids wasting bandwidth on redundant fields. Some players can actually output a true 24fps signal, you do need a compatible display device though.
Bob.
Infinite5ths wrote on 12/29/2005, 1:46 PM
OK farss,

That makes a lot of sense. I never considered how pulldown would affect FX (no play on words intended). I guess that comes from having a slow PC that doesn't handle lots of effects processing (audio or video) with any elegance.

I'm still a bit mystified by CourseDesign's comment about the external TV though. I've lurked here enough to know that he often condenses his extensive knowledge into very brief posts. His wisdom in this one is just still a bit beyond my grasp. :-]

You mentioned (as I expected) that pulldown would have to be added to display a 24p Vegas project on an external (interlaced) TV. One question: Where is the pulldown added?

a) Before being sent to the FireWire output stream

b) In the digital-to-analog pass-through device

c) Somewhere else

My guess is "a", based on what was said earlier about DV -- it only is stored as an INTERLACED format. I assume that means it's also TRANSFERRED as an interlaced stream (i.e. field by field, not frame by frame). [If it's being transferred via FireWire, do the terms "progressive" and "interlaced" even apply?]
--
Mike
farss wrote on 12/29/2005, 1:51 PM
External TVs wouldn't accept a 24p signal, don't even know of a D->A converter that will. So if you are using an external TV or monitor as a preview device pulldown has to be added for the benefit of that device.
Using the 'external' 2nd monitor option in V6 avoids that though.
Bob.
Infinite5ths wrote on 12/29/2005, 1:56 PM
...you mean the 2nd external CRT/LCD monitor option? (i.e. another progressive scan computer monitor, instead of a TV).

Note: I edited my post above to add another question. You partially answer it in your most recent post.
--
Mike
Coursedesign wrote on 12/29/2005, 2:48 PM
...you mean the 2nd external CRT/LCD monitor option? (i.e. another progressive scan computer monitor, instead of a TV).

The external VIDEO previewing device (can be a video CRT, video LCD, or a computer LCD with video inputs, etc.), as opposed to a 2nd Windows monitor used to extend the Windows desktop.

Bob said it right re TVs being unable to accept 24 frames per second, they need the 30i (also referred to as 60i) for NTSC.
Infinite5ths wrote on 12/29/2005, 9:12 PM
Thanks for the help folks. I'm sorry I disappeared for a while there. I finally got around to buying an external FW hard disk to use as a backup for my two internal drives. Up to now, one of the drives (they are identical) was in a removable rack, used with Ghost as a backup-only drive. The other handled everything (OS, programs, projects, page file, etc.). Now they are both installed in the drive rack, one as a system drive, the other as a project drive -- with the FW drive for backup.

At any rate.....I think I'm all clear on the 24p DV issue. The terminology just threw me for a loop.
--
Mike