Pull down cadence if that's the right terminology?

If they had mixed footage (interlaced and progressive) that might be a reason. Otherwise, if the destination is DVD, and the footage is progressive, I can't really see why you wouldn't want to do it with a 23.976 fps GOP.
 
Any authoring program that can accept a .m2v (fundamental MPEG stream) can utilize any compliant GOP structure, including one that is based upon a 24 fps flagged structure. What low end authoring software may be incapable of accomplishing is encoding (MPEG encoding) a 24 frame GOP structure from within their own application. Typically, much more control over the project can be had by encoding outside of the authoring program. DVD authorhing actually consists of two major parts, one is the encoding (often referred to as transcoding) the other is the creation of the PGCs and associated menus (still shows, motion menus and sub pictures).

Higher end authoring systems can break the authoring process into a number of different sub applications; in the case of Encore, you can accomplish much of the menu creation in PhotoShop.
 
It depends on the NLE as to whether you shoot ADVANCED or NORMAL. ADVANCED was developed to make it easier for DV native editing systems to work at native 23.976 rate. But Avid Xpress Pro (and most likely others) can capture both ADVANCED and NORMAL directly over FireWire. There is an argument that NORMAL requires a decompress and recompress of the DV stream, but so does every render you thereafter (color corrections, effects work, etc. The only way to avoid that is to capture from DV to an uncompressed SD format over SDI or decompressed from the DV stream and saves as 1:1.

Michael
 
GOP = Group Of Pictures. It is the term for the elements that make up an MPEG stream. There are three different types of "Pictures" or frames within a GOP.

I or Intra coded frames. These are the only frames that are independent and contain a complete image. In most GOPs, these occur only twice per second.

P or Predictive frames. These frames occur in a pattern (determined by the encoding software) between I frames. P frames contain only the motion vectors (difference between the current and previous I frame). These frames are not independent (do not generate a complete picture or frame on their own) but require much less bandwidth than an independent I frame.

B or bidirectional frames. These frames can also occur in a pattern (determined by the encoding software) between the I frames. B frames, like P frames contain only a small portion of the picture and use both the previous and subsequent frames to generate their content. B frames are also not independent, also require much less bandwidth than I frames but require more processing (both during encoding and decoding) than P frames as they utilize more frames to support their content.

A valid GOP is not obligated to use any B frames, and could consist of only I and P frames, and some lower performance encoders will exclude any B frames from their GOP to reduce the encoding processing burden. This usually yields a lower performance (poor looking) MPEG stream for the same average data rate as one that used all three frame or "Picture" types.

A typical pattern for an NTSC frame would be:

IBBPBBPBBPBBPBBI... (for 1/2 second of a 29.97 f/s rate)

or

IBBPBBPBBPBBI... (for 1/2 second of a 23.976 f/s rate)

The advantage being that there are 3 fewer (1 fewer I and 2 fewer B frames) frames encoded, so with the same average data rate, the 23.976 GOP structure can have higher data rates for each frame (for better quality) or lower data rate for the same quality (but longer playing time).
 
Thanks for the thorough definition. MichaelP - can you tell me more about "The only way to avoid that is to capture from DV to an uncompressed SD format over SDI or decompressed from the DV stream and saves as 1:1". When we're talking about SD and SDI, who is using this for what reason and with what products?
 
Okay so after reading the thread on Andromeda product for the DVX100a, I think I understand a little bit of what is meant by "uncompressed" DV.
 
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