Video clock and framing signal extraction by transport stream “snooping”

• US 6,330,285 B1
• Filed: 02/11/1998
• Issued: 12/11/2001
• Est. Priority Date: 02/11/1998
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Van Dusen, Charles H., Prasannan, Venkataraman, Crosby, Philip S., Gimlett, James L.
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): PHILIPPE, GIMS S
• Application Number:
  US09/021,620
• Time in Patent Office: 1,399 Days
• Field of Search: 348/845.2, 348/423, 348/565, 348/419, 348/464, 348/425.4, 348/425.2, 348/845.3, 348/423.1, 371/47.1, 370/509, 370/468, 370/516, 370/253, 370/395, 370/473, 375/376, 375/368, 375/240.28, 375/240.27
• US Class Current: 375/240.28
• CPC Class Codes: H04N 19/00 Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/4348 Demultiplexing of additional data and video streams
• CPC Class Codes: H04N 21/64307 ATM
• CPC Class Codes: H04N 7/56 Synchronising systems therefor

Abstract

An apparatus for video clock and framing signal extraction by transport stream snooping parses MPEG2 Transport Packet headers from a transmission transport stream and partially decodes the headers to identify those corresponding to a specified packet identification (PID). From the specified headers a program clock is decoded and compared with a recovered program clock generated by a local clock oscillator and a local clock counter. The comparison is used to finely tune the recovered program clock frequency. Also from the heads video framing information is decoded, and such framing information and the recovered program clock are used to generate a video reference signal.

Claims

1. An apparatus for recovering a video clock from a transport stream containing digital data including MPEG Transport Packets without buffering any of the transport stream digital data and without full MPEG decoding comprising:

means for extracting MPEG Transport Packet headers from the digital data transport stream;

means for partially parsing from the MPEG Transport Packet headers which have a reference packet identification code only a program reference clock and a presentation time stamp;

means for comparing the program reference clock with a local clock to generate a recovered program clock; and

means for generating from the presentation time stamp and the local clock the video clock.

2. The apparatus as recited in claim 1 wherein the partially parsing means comprises:

means for identifying the MPEG Transport Packet headers having the reference packet identification code; and

means for extracting the program reference clock from an appropriate one of the identified MPEG Transport Packet headers.

3. The apparatus as recited in claim 1 wherein the comparing means comprises:

an oscillator operating at a nominal frequency and having a control input, the oscillator providing the local clock as an output;

a counter having the local clock as an input and the recovered program clock as an output; and

a comparator having the recovered program clock and program reference clock as inputs to generate a control signal that is coupled to the control input of the oscillator to finely tune the oscillator.

4. The apparatus as recited in claim 3 wherein the generating means comprises a genlock circuit having the local clock signal and the presentation time stamp as inputs and providing the video clock as an output.