In an earlier post, I described some of my findings with respect to cadence breaks and changes in 2:3 pulldown flag patterns on commercial DVD discs.

I went back to some very early (circa 1992) literature on the development of the MPEG-2 standard, and found some references to the motivations for the 2:3 pulldown features of MPEG. As it turns out, the designers of MPEG-2 anticipated these choppy cadences of 2:3 pulldown material as such sequences are commonly produced by non-linear editing systems when the final product is 29.97i.

So this brings my understanding full circle. The first time I noticed breaks and changes in 2:3 pulldown flags was in evaluating and comparing two different releases of a Hollywood DVD: the original theatrical release vs. the directors cut.

It was clear that the director's cut was reworked on a non-linear editing system, and then released straight to DVD. They probably did the director's cut in 29.97i, using additional 2:3 telecine material (ie. scenes not in the theatrical release). This would account for the fact that 99% of the DVD has a regular 2:3 pulldown cadence and just a very few scenes have true 29.97i material.

Nevertheless, DVD discs which contain mixed pulldown cadences will undoubtedly cause a great deal of trouble for people ripping discs and re-encoding.