HD workflow: posting high defintion without jitters - High Def

Post, Feb, 2004 by Claudia Kienzle

In December 1995, when the FCC mandated the nation's transition from NTSC to ATSC, they left the choice of over 18 approved high defintion and standard definition formats to broadcasters, who went ahead and picked different ones for use on their networks. Since then, those doing editing and mastering for television or digital film markets have faced a veritable Tower of Babel, where formats of different resolutions, frame rates, aspect ratios and scanning types need to co-exist, often in a single project. While editors can stay sane when working in any one format, the real madness starts when they must mix media--typically cutting 29.97fps interlaced 4:3 NTSC with 16:9 HD formats like 720/60p, 1080/30i and 1080/24p. The most common scenario impacting workflow is when acquisition or final mastering is at 24fps progressive HD (24p HD), but the of-fline NLE still takes 29.97fps interlaced NTSC.

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When cross-converting between different formats and frame rates, editors say it's common to encounter headaches, such as audio that's slightly out of sync or edit events that are a few frames off. But, now that the transition is well underway, things are getting better because editors have amassed greater experience dealing with cross-conversion issues. And next-generation editing and format conversion systems increasingly offer built-in support for the new universe of ATSC formats.

FRAME-RATE CONVERSIONS

"When you talk about HD workflow issues, the biggest problems invariably involve frame-rate conversions," says Scott Thomas, director of engineering for Victory Studios (www.victorystudios.com) in Seattle. (Victory also has an LA studio.) "Despite the manufacturers' hype, there is no perfect format converter that won't introduce artifacts, especially for complex conversions such as 29.97fps interlaced NTSC to 24p HD. Also, changes in frame rates can affect the length of the program, change the pitch of the audio or introduce motion jitter or extended edit events if not done properly."

If source video has been captured at different formats or frame rates, Thomas adds, "We advise our clients to convert all their footage to the format they will be editing in. They should also evaluate the quality of the resulting video prior to entering the edit suite. If clients are seeing their upconverted HD material on an HD monitor for the first time after the edit session has begun, the discovery of an artifact or motion defect can slow progress or halt the session altogether while fixes are explored."

"If you're offlining a project at 29.97fps interlaced NTSC and expect to bring that EDL to a 1080/24p HD online, it's also cost effective to put the EDL through a conversion program, such as Software Grille, that will identify and smooth out timing issues due to changes in frame rates before executing the conform," says Walt McGinn, editor for Post Solutions/Victory Studios (www.postsolutions.com) in LA. [Editor's Note: Post Solutions and Victory Studios have merged administrative operations into one facility--while still maintaining separate identities.]

McGinn recently did the online editing, plus some color correction and sweetening for The Book of Mormon Movie, Volume 1: The Journey. Shot in 24p HD, the feature was offlined at 29.97fps NTSC and then onlined in 24p HD at Victory Studios, Seattle, for output to 35mm film.

There are also pitfalls to avoid. If you are cutting archival video, transferred from film to 29.97fps interlaced NTSC and then incorporating that video with 1080/24p, there are instances where a "double 3:2 pull-down" could result. "This is because the legacy video already has a 3:2 pull-down that was inserted during the original film transfer," Thomas says. "But now as part of the 1080/24p master, it could be subjected to a second 3:2 pull-down in subsequent conversions, which would cause noticeable motion timing problems."

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4:3 TO 16:9

"Whenever you're mixing SD and HD formats, you're bound to face many artistic and technical challenges," says Alex Catchpoole, VFX supervisor for Guava (www.guavanyc.com) in New York. "While 35mm film and SD video have a relatively square 4:3 image, HD has a rectangular 16:9 shaped image--and this difference affects the picture composition when converting content from one aspect ratio to the other."

Also, Guava's visual effects technical supervisor, Ari Zohar Kling-man, adds, "Since video is shot at 29.97 fps [or 60 individual fields per second interlaced], this frame rate must be reduced to 24fps progressive for a film or 24p HD product. And, since fixes like 3:2 pull-down only apply to video originated on film or at the film frame rate, it's necessary to field average the video to progressive scan and then reduce the timing. These conversions can produce artifacts which, when the resolution is increased to HD or film, can be extremely noticeable."

Klingman and Catchpoole tackled these conversion challenges in the HD post and mastering of video integral to Sinatra: His Voice. His World. His Way. A theatrical production at Radio City Music Hall in New York (which opened October 2003), Sinatra: His Voice. His World. His Way featured film and video from Frank Sinatra's stage, screen and television performances, along with video clips of entertainers like Bruce Willis, Luciano Pavarotti and Elvis Costello talking about Sinatra.