So one day I had the new version of MPressionist.X Pro running while I was working on something else. I had the director's cut of a Hollywood DVD playing. This is a teen comedy; I believe the director's cut went straight to DVD. One of the reason's I was analyzing the disc is because it is available both as a director's cut and a regular disc. To compare, you see.

So there I am working in another program, and out of the corner of my eye I saw what appeared to be a frame containing two fields of video flash by. Now, this disc is a full progressive feature originating on film, so my interest level went way, way up. I hit pause and backtracked a bit and looked through the frames, and sure enough, there was a sequence of about 4-6 frames which were standard 29.97 interlaced NTSC source material. The picture was fast-moving and so the fields were completely evident.

Not only were there several frames of oddball footage in this section of the movie, but as well, the 2:3 pulldown cadence, which is simply a series of 2-bit flags in the bitstream, would have broken down. Over the next few weeks I wondered how many Hollywood titles contained MPEG-2 video which was a combination of 2:3 pulldown 23.976x720x480p and 29.97x720x480i.

I decided to add a new feature to the new MPressionist.X Pro: one that would allow you to 'see' any irregularities in the field dominance (including 2:3 pulldown patterns) over the entire duration of the movie.

One interesting thing about changes to the 2:3 pulldown cadence: it can potentially cause problems for a DVD mux that is expecting the footage to be uniform. A frame that is part of a 2:3 pulldown has a fixed duration. As soon as you start mixing 2:3 and 29.97i you have encoded pictures with a mixture 3/2 and 2/2 durations. The math is simple, but the effects on the timing in the mux over a 2 hour feature would be considerable and could account for all sorts of problems, including audio-video sync drift and whatnot.

Nevertheless, in building this new feature a fairly wide vista of possibilities for reporting errors in the bitstream opened up. Adding a feature is never as easy as it first appears to be.

As it turns out, many Hollywood titles contain breaks in the 2:3 pulldown pattern. However, many titles are perfect: no breaks, just pure 720x480p all the way through.