Managing lip sync
Sep 1, 2007 12:00 PM, BY ALDO CUGNINI
Technological progress often seems to occur haltingly: two steps forward, one step back. With the advent of digital processing, video processing began
Several units can correct varying delays automatically, such as the Pixel AD3100 audio delay and synchronizer, which provides compensation based on a control input from a compatible video frame synchronizer. It can also automatically correct independent variable delay sources by interfacing with the company's DD2100 video delay detector, which samples the video at two points in a system and then provides a control signal to the AD3100 audio delay unit. Similarly, the Sigma Electronics Arbalest system uses a proprietary technology to provide automatic video delay detection and audio compensation in a system.
Industry activities to address solutions
Aside from a handful of proprietary solutions, no standard solution has yet been described. It is becoming apparent that end-to-end solutions are needed, and several trade groups are actively studying the problem. SMPTE has created, within the S22 Committee on Television Systems Technology, an Ad Hoc Group on Lip Sync Issues to address the problem and produce guidelines documents. Work on a coordinated studio-centric solution will probably include problem assessment, current practices, control signals, and known and potential solutions.
The Pixel Instruments LipTracker uses a proprietary system to measure video delays.
The ATSC's recently developed strategic plan notes that although the AC-3 digital audio standard is mature, implementations have varied, in particular with regard to lip sync and sound levels. The ATSC Technology and Standards Group on Video and Audio Coding (TSG/S6) has thus been directed to look into these issues, and has established two working groups to gather implementation data and report back with recommendations. It is believed that the group will coordinate with SMPTE and concentrate on emission stream issues.
Other groups are studying the issue, as well. In Canada, World Broadcasting Unions International Satellite Operations Group (WBU-ISOG) has conducted tests on satellite encoders and decoders. An EBU audio group has performed tests for SDTV receivers. In Japan, the Japan Electronics and Information Technology Industries Association (JEITA) IEC-TC100 has started investigations on TV receiving devices.
The entire problem is quite complex when one also considers the effects of editing, voice-overs and other routine operations. In addition, practical feedback to controlling systems must be developed, or an unstable condition could be created. Beyond the technical issues, there exists the potential for technical (and legal) disagreements. Let's hope that the motivation for a better viewer experience trumps that and provides a genuine improvement.
Aldo Cugnini is a consultant in the digital television industry.
Send questions and comments to: aldo.cugnini@penton.com
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