Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-02-11
2001-12-11
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C370S509000
Reexamination Certificate
active
06330285
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
The present invention relates to compressed video systems, and more particularly to video clock and framing signal extraction from a compressed video transport stream by “snooping”.
Video and related signals now may be interrelated through their inclusion as members of a functional group. An example is the “Transport Stream” syntax described in ISO/IEC 13818-1, commonly known as the MPEG-2 Stream specification. While this standard describes a means of separating these component or elementary signals and extracting a timebase that may be common to them, video and audio facilities may have a requirement that has greater scope—the synchronization of most or all signals within the facility with a selected incoming or outgoing Program Stream.
In a large facility the place where a given Transport Stream is likely to be decoded is uncertain, and may change according to the tasks being performed within that facility. Furthermore the cost of fully decoding such a stream is considerable.
The content of video production facilities is expected to pass through a network interface device (NID) connecting that facility to a more general telecommunication network. Such a network is likely to use some form of asynchronous, packet-based protocol such as Asynchronous Transfer Mode (ATM). This uncovers an additional need—that of determining for network management purposes the errors in the arrival times of incoming ATM packets.
What is required is an economical means of providing a unified timing means at a content facility and of providing data that may be used for intelligent network management.
BRIEF SUMMARY OF THE INVENTION
Accordingly the present invention provides for video clock and framing signal extraction by Transport Stream “snooping”. A transmission transport stream, such as an Asynchronous Transfer Mode (ATM) transport stream, is parsed to extract MPEG-2 Transport Packet headers. The extracted headers are partially decoded to identify those having a reference packet identification. From the identified headers a program clock is decoded and compared with a recovered program clock generated from a local clock oscillator and local clock counter. The comparison serves to finely tune the local clock oscillator about a nominal frequency, such as 27.000 Mhz. The recovered clock frequency may be used for facility timing, and may be used together with framing information decoded from the headers to generate a reference video signal such as a genlock signal.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.
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Crosby Philip S.
Gimlett James L.
Prasannan Venkataraman
Van Dusen Charles H.
Gray Francis I.
Kelley Chris
Philippe Gims
Tektronix Inc.
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