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The Moving Picture: Authoring SD-DVDs for an HD/LCD World
Posted Dec 21, 2010 Print Version     Page 1of 1

I spent a week in December working with a contracting firm that provides video services to a large U.S. government agency. It was a very high-tech group, with broadcast-quality gear and talent, and it was interesting to see the breadth of productions that the group members support, from live events to training materials to videos in support of the agency’s technology initiatives. It was also interesting to see the breadth of outputs that they supported, from very high-quality H.264 files uploaded to their online video platform (OVP) for internet use, to WMV/lower-quality H.264 video for integrating into PowerPoint, and lots and lots of DVDs.

Before working with this firm, it had been a while since I had actually developed any DVD production-related training. After talking with the group during the preparatory phase of the training, it quickly became obvious that while DVD technology hasn’t changed in a while, the changes around it have significantly impacted both production workflows and playback environments. For example, by agency mandate, the group shoots in 720/60p, which means 60 full-resolution 1280x720 frames per second. The 60p mandate wasn’t designed to create the “filmic” look; rather, with their scientific bent, the group chose this format because it captured the most information at the highest quality. For example, their cameras supported 1080p, but only at a maximum of 30p, which meant 30 discrete video impressions a second. Though the frames are smaller, they wanted the 30 extra full impressions they were able to achieve with 720/60p.

However, to format 720/60p for standard-definition 480- line DVD, you have to convert it to 720x480 resolution video at any number of scan rates, both progressive and interlaced. You get the smoothest result at 29.97i, since you map each 60p frame to a 29.97i field, preserving the 60 impressions per second, albeit at a much lower resolution. Anyway, one problem that we focused on related to a long shot of a spokeswoman walking around a studio. In postproduction, they were inserting faux LCD screens displaying different videos, which is why they shot a long shot rather than a medium or closeup. The shot looked great at 720/60p, but after downsampling and interlacing for a 29.97i SD DVD, the woman’s face shimmered from the interlacing on the huge plasma display they used for previewing. The shimmering was brief and the client in the agency didn’t notice it, but the producers wanted to eliminate it.

The solution that they came up with was very creative: producing at 24p rather than 29.97i. As you probably know, 24p is a legal format for DVDs, and eliminating the interlacing got rid of the shimmer. The only problem was that the panning in the sequence looked a lot less smooth than the original 60p video, or even the 29.97i video. That’s because with either 60p or 29.97i, the viewer sees 60 distinct, regularly spaced impressions a second. Since 24 doesn’t divide into 60 evenly, the cadence after the 60p to 24p conversion is uneven (drop one frame, show a frame, drop two frames, show a frame, drop one frame, etc.). Though you can use interpolation techniques to smooth the motion, the result is never as smooth as rendering 60p video at 29.97i or what you would have achieved by shooting at native 24p.

We noodled for a bit, and I suggested that we convert from 60p to 29.97i in Adobe After Effects rather than Apple Final Cut Pro or Adobe Media Encoder, which they had previously tried. No dice: The shimmering was a little less noticeable, but it still was nowhere near as clear as the 24p video. Then someone suggested producing at 30p. I was skeptical since—as far as I knew—30p wasn’t a legal format for DVD. We gave it a shot, though, and DVD Studio Pro loaded the file without re-rendering, definitely a good sign.

We burned a DVD containing all the alternatives—29.97i, 29.97i from After Effects, 24p, and 30p—and the 30p looked as clear as the 24p, but smoother. We had a winner, at least on the big plasma screen.

Then we took the DVD around and played it on a number of other target platforms, including an old NTSC CRT monitor and Mac and Windows computers. What was shocking to me was how different the video looked on all of the playback platforms. The NTSC CRT monitor was the most forgiving, displaying the interlaced and progressive video with no shimmering or noticeable interlacing-related artifacts, and, of course, at 29.97i the video was very smooth. The big plasma was the least forgiving. The shimmering and interlacing was very obvious in the interlaced modes, and the motion was very jerky. The computer screens were somewhere in the middle, with the shimmering noticeable, though not terrible, but the interlaced lines were very noticeable.

This agency generally produces fairly short videos, and one idea was to produce two versions: one progressive at 30p and one interlaced at 29.97i, letting the viewer decide which looked best on his or her playback platform. Bridging over to what we do for a living, if I were producing a wedding video, I would definitely want to know the primary playback platforms for the resulting video. I’ve always produced for DVD exclusively in 29.97i, but as the market transitions from CRTs to plasma, LCD, and OLED displays, I definitely want to understand how my interlaced productions look before I shoot, edit, and render at 29.97i.

Jan Ozer (jan at doceo.com) is a frequent contributor to industry magazines and websites on digital video-related topics. He is chief instructor at StreamingLearningCenter.com.

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