Split-Screens: The New Way to Tighten an Edit
Maybe you saw some of the DVD behind-the-scenes or promotional material created for Adobe TV about postproduction on David Fincher's feature The Social Network. The rapid pace of this dialog-heavy movie wasn't just the result of tight writing or a fast-speaking Jesse Eisenberg; many scenes containing dialog were tightened via compositing, perhaps the most useful technique to take a story-driven editor into After Effects.
The only way to tighten a scene with a lot of dialog in the NLE is with a lot of cutting, which presumes that a) you have a good deal of coverage to cut away to, and even more importantly, b) cutting away from the master shot is appropriate. Cutting to a reaction or closeup changes the emotion of the scene; it can break the tension created by a master shot.
The alternative is simple in concept. For example, given a shot of dialog with actor A on the left and actor B on the right, you add a mask separating the shot into two, so that frames can be removed from each side of the shot to tighten the pacing. The timing of the line delivered by actor B in response to actor A can be tightened within the same shot (see Figures 4a and 4b).
Figure 4b Here's the simplest possible setup for splitting A/B dialog, at least until you see the camera move; the seam provided by the window frame is an easy dividing point to conceal. The reaction of the character on the other side is rolled back so that the response appears quicker than it actually was when shot. Before (Figure 4a) and after (Figure 4b) of splitting this screen neatly down the middle and slipping the timing so that the man on the right begins his next line earlier.
Even if the camera is static, covering the seams with such a technique is beyond what most editing programs can do—and there's almost never such a thing as a truly static scene. In addition to being proficient with masks, selections, and retiming, you'll need a few techniques to cover the seams: retiming effects, motion tracking, paint, and even the occasional bit of morphing or warping. Although I don't mention this specific technique in Adobe After Effects CS6 Visual Effects and Compositing Studio Techniques, I cover in depth all of those building blocks for creating such a shot.