Video and audio synchronization

Interactive video distribution systems – Video distribution system with local interaction

Reexamination Certificate

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Details

C348S515000, C348S518000, C348S180000, C348S192000

Reexamination Certificate

active

07020894

ABSTRACT:
In order to synchronise video and audio signals, a video test signal and an audio test signal are generated at the transmitting end of a transmission link, and transmitted over the link. The video test signal has first and second active picture periods of contrasting states. The audio test signal has first and second periods of contrasting states. As generated, the video and audio test signals have a predetermined timing relationship—for example, their changes of respective states may be coincident in time. At the receiving end of the link, the video and audio test signals as received are detected, and any difference of timing between the video and audio test signals is derived from their changes of respective states, measured and displayed, including an indication of whether the video signal arrived before the audio signal or vice-versa. Additionally or alternatively, such a measurement signal can be used in a control loop to compensate for the delay and automatically re-synchronise the audio and video signals. The system is particularly suitable for transmission of video and audio over separate paths of a link—e.g. respectively over satellite and terrestrial paths.

REFERENCES:
patent: 4689676 (1987-08-01), Nakajima et al.
patent: 4703355 (1987-10-01), Cooper
patent: 4963967 (1990-10-01), Orland et al.
patent: RE33535 (1991-02-01), Cooper
patent: 5550594 (1996-08-01), Cooper et al.
patent: 0 386 928 (1990-09-01), None
patent: 2 282 929 (1995-04-01), None
Patent Abstracts of Japan, vol. 012, No. 153 (E-607), May 11, 1988.

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