Frame synchronization in an ethernet NTP time-keeping digital cinema playback system

• US 7,448,061 B2
• Filed: 06/21/2004
• Issued: 11/04/2008
• Est. Priority Date: 06/21/2004
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Richards, Martin John, Lemieux, Pierre-Anthony Stivell, Mandell, Douglas Evan, Karanjkar, Makarand Prabhakar
• Primary Examiner(s): Grant; Christopher
• Assistant Examiner(s): SCHNURR, JOHN R
• Application Number:
  US10/873,407
• Publication Number:
  US 20050283820A1
• Time in Patent Office: 1,597 Days
• Field of Search: 348/422.1, 348/518, 352/85, 370/498, 370/503, 370/519, 709/204, 709/205, 709/248, 725/80, 725/82, 725/112, 725/116
• US Class Current: 725/82
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04N 21/41415 involving a public display, viewable by several users in a public space outside their home, e.g. movie theatre, information kiosk
• 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 21/4341 Demultiplexing of audio and video streams
• CPC Class Codes: H04N 21/436 Interfacing a local distribution network, e.g. communicating with another STB or one or more peripheral devices inside the home
• CPC Class Codes: H04N 21/4405 involving video stream decryption
• CPC Class Codes: H04N 21/6125 involving transmission via Internet transmission by internet of broadcast information H04H60/82

Abstract

In a digital cinema network of NTP-timekeeping devices in which one of the devices decodes video information, the scheduling of future instructions takes into account the differences between the nominal and actual frame rates of the video decoding device and the network'"'"'s NTP latency.

Claims

1. In a digital cinema network of NTP-timekeeping devices, the network having a variable, but expected maximum, latency among its devices, one of the NTP-timekeeping devices decoding video information, which video information has a nominal frame rate, at an actual frame rate determined by a clock that is not locked to the network NTP time, the network having a schedule of instructions to be performed at one or more future frame times by one or more devices on the network, wherein the schedule'"'"'s future NTP times corresponding to such future frame times are initially based on said nominal frame rate, a method of instructing said one or more devices with improved frame accuracy, comprising

adjusting one or more of the future NTP times in said schedule of instructions in response to a measure of the actual frame rate, and

sending at least one NTP-time-adjusted instruction to at least one device on the network, wherein the adjusted NTP time or times of the at least one instruction is or are at least as far in the future as the expected maximum network time latency.

2. A method according to claim 1 wherein said adjusting is performed repetitively.

3. A method according to claim 2 wherein said adjusting is performed every frame.

4. A method according to claim 1 wherein all future NTP times in the schedule are adjusted at least once.

5. A method according to claim 4 wherein all future NTP times in the schedule are adjusted repetitively.

6. A method according to claim 5 wherein all future NTP times in the schedule are adjusted every frame.

7. A method according to claim 1 wherein said devices include an automation interface device and said sending sends at least one NTP-time-adjusted instruction to the automation interface device.

8. A method according to claim 7 wherein said sending sends at least one NTP-time-adjusted instruction only to the automation interface device.

9. A method according to claim 1 wherein said measure of the actual frame rate is based at least in part on at least one frame-time-to-NTP-time relationship subsequent to the start of the video information.

10. Apparatus comprising:

memory; and

processing circuitry coupled to the memory, wherein the processing circuitry is adapted to perform the methods of any one of claims 1 through 8.

11. A computer program, stored on a computer-readable medium for causing a computer to perform the methods of any one of claims 1 through 8.

12. In a digital cinema network of NTP-timekeeping devices, the network having a variable, but expected maximum, latency among its devices, one of the NTP-timekeeping devices decoding video information, which video information has a nominal frame rate, at an actual frame rate determined by a clock that is not locked to the network NTP time, the network having a schedule of instructions to be performed at one or more future frame times by one or more devices on the network, wherein the schedule'"'"'s future NTP times corresponding to such future frame times are initially based on said nominal frame rate, a method of instructing said one or more devices with improved frame accuracy, comprising adjusting one or more of the future NTP times in said schedule of instructions in response to at least one frame-time-to-NTP-time relationship subsequent to the start of the video information at said nominal frame rate, and

sending at least one NTP-time-adjusted instruction to at least one device on the network, wherein the adjusted NTP time or times of the at least one instruction is or are at least as far in the future as the expected maximum network time latency.

13. A method according to claim 12 wherein said adjusting is performed repetitively.

14. A method according to claim 13 wherein said adjusting is performed every frame.

15. A method according to claim 12 wherein all future NTP times in the schedule are adjusted at least once.

16. A method according to claim 15 wherein all future NTP times in the schedule are adjusted repetitively.

17. A method according to claim 16 wherein all future NTP times in the schedule are adjusted every frame.

18. A method according to claim 12 wherein said devices include an automation interface device and said sending sends at least one NTP-time-adjusted instruction to the automation interface device.

19. A method according to claim 18 wherein said sending sends at least one NTP-time-adjusted instruction only to the automation interface device.

20. Apparatus comprising:

memory; and

processing circuitry coupled to the memory, wherein the processing circuitry is adapted to perform the methods of any one of claims 13 through 19.

21. A computer program, stored on a computer-readable medium for causing a computer to perform the methods of any one of claims 13 through 19.

22. In a digital cinema network of NTP-timekeeping devices, the network having a variable, but expected maximum, latency among its devices, one of the NTP-timekeeping devices decoding video information, which video information has a nominal frame rate, at an actual frame rate determined by a clock that is not locked to the network NTP time, the network having a schedule of instructions to be performed at one or more future frame times by one or more devices on the network, wherein the schedule'"'"'s future NTP times corresponding to such future frame times are initially based on said nominal frame rate, a method of instructing said one or more devices with improved frame accuracy, comprising

instructing said one or more devices based on a measure of the actual frame rate, wherein each instruction is for an NTP time at least as far in the future as the expected maximum network time latency.

23. A method according to claim 22 wherein said measure of the actual frame rate is based at least in part on at least one frame-time-to-NTP-time relationship subsequent to the start of the video information.

24. In a digital cinema network of NTP-timekeeping devices, the network having a variable, but expected maximum, latency among its devices, one of the NTP-timekeeping devices decoding video information, which video information has a nominal frame rate, at an actual frame rate determined by a clock that is not locked to the network NTP time, the network having a schedule of instructions to be performed at one or more future frame times by one or more devices on the network, wherein the schedule'"'"'s future NTP times corresponding to such future frame times are initially based on said nominal frame rate, a method of instructing said one or more devices with improved frame accuracy, comprising

instructing said one or more devices in response to at least one frame-time-to-NTP-time relationship subsequent to the start of the video information at said nominal frame rate, wherein each instruction is for an NTP time at least as far in the future as the expected maximum network time latency.