Time synchronization of media playback in multiple processes

• US 8,321,593 B2
• Filed: 06/28/2007
• Issued: 11/27/2012
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Bushell, John Samuel, Chapman, Gregory R., Batson, James D.
• Primary Examiner(s): Chan, Wing
• Assistant Examiner(s): KATSIKIS, KOSTAS J
• Application Number:
  US11/823,670
• Publication Number:
  US 20080168470A1
• Time in Patent Office: 1,979 Days
• Field of Search: 709/248, 719/313, 718/107, 713/500, 713/375
• US Class Current: 709/248
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04L 69/28 Timers or timing mechanisms used in protocols
• CPC Class Codes: H04N 21/2368 Multiplexing of audio and video streams
• CPC Class Codes: H04N 21/43072 of multiple content streams on the same device
• CPC Class Codes: H04N 21/4341 Demultiplexing of audio and video streams
• CPC Class Codes: H04N 21/8547 involving timestamps for synchronizing content
• CPC Class Codes: H04N 7/52 Systems for transmission of a pulse code modulated video signal with one or more other pulse code modulated signals, e.g. an audio signal or a synchronizing signal assembling of a multiplex stream by combining a video stream with other content or additional data, remultiplexing of multiplex streams, insertion of stuffing bits into the multiplex stream, assembling of a packetised elementary stream at server side H04N21/236; disassembling of a multiplex stream, remultiplexing of multiplex streams, extraction or processing of Service Information, disassembling of packetised elementary stream at client side H04N21/434

Abstract

Systems, methods, devices that enable the efficient synchronization of timing information from first time-based process to a second time-based process using periodic or event-driven synchronization messages are provided. In one aspect, the invention includes a media processing system having a first process for processing media based, at least in part, on first timing information derived from a first timing source and a second timing source. The system may also include a second process for processing the media based, at least in part, on second timing information derived from the first timing source. The first process may send one or more timing synchronization messages, generated based at least in part on the first timing source and the second timing source, to the second process to synchronize the second timing information with the first timing information.

Claims

1. A media processing system comprising control circuitry configured to:

execute a first process for processing media, wherein the first process accesses a first timing source and a second timing source, and wherein the first process processes media based at least in part on first timing information derived from the first timing source;

execute a second process for processing the media, wherein the second process accesses the second timing source but cannot access the first timing source, and wherein the second process processes media based at least in part on shadow timing information;

wherein the first process sends one or more timing synchronization messages, generated based at least in part on the first timing source and the second timing source, to the second process to synchronize the second process with the first process; and

wherein the shadow timing information is an estimate of the first timing information maintained by the second process.

2. The system of claim 1, wherein each synchronization message is sent periodically.

3. The system of claim 1, wherein each synchronization message is sent in response to an event.

4. The system of claim 3, wherein the event includes the receipt, by the first process, of a media processing instruction.

5. The system of claim 4, wherein the media processing instruction includes at least one of play, pause, fast forward, reverse, and stop.

6. The system of claim 5, wherein the media processing instruction is delivered to the first process from a third process.

7. The system of claim 1, wherein the timing synchronization message includes at least one time stamp associated with the first timing information derived from the first timing source.

8. The system of claim 1, wherein the timing synchronization message includes at least one of a time stamp from a base clock of the first timing source, a time stamp from a base clock of the second timing source, a time stamp from a time base associated with the first process, a rate associated with the time base, and a rate scaler between the first and second timing sources.

9. The system of claim 1, wherein the shadow timing information is derived from the second timing source.

10. The system of claim 9, wherein the second timing source includes a common reference clock.

11. The system of claim 1, wherein the first timing information comprises at least one of a base clock of the first timing source and a first movie time base derived from the base clock of the first timing source.

12. The system of claim 11, wherein the shadow timing information comprises at least one of a first shadow time base estimating the base clock of the first timing source and a second shadow time base estimating the first movie time base.

13. The system of claim 12, wherein the first shadow time base and the second shadow time base continuously estimate the base clock of the first timing source and the first movie time base respectively.

14. The system of claim 1, wherein the first timing source includes an audio clock.

15. The system of claim 1, wherein the control circuitry is further configured to synchronize the second process with the first process by updating the shadow timing information based at least in part on the received synchronization messages.

16. A personal media device comprising a processor configured to:

execute a first process for processing media, wherein the first process accesses a first timing source and a second timing source, and wherein the first process processes media based at least in part on first timing information derived from the first timing source;

execute a second process for processing the media, wherein the second process accesses the second timing source but cannot access the first timing source, and wherein the second process processes media based at least in part on shadow timing information;

wherein the first process sends one or more timing synchronization messages, generated based at least in part on the first timing source and the second timing source, to the second process to synchronize the second process with the first process; and

wherein the shadow timing information is an estimate of the first timing information maintained by the second process.

17. The device of claim 16, wherein each synchronization message is sent periodically.

18. The device of claim 16, wherein each synchronization message is sent in response to an event.

19. The device of claim 18, wherein the event includes the receipt, by the first process, of a media processing instruction.

20. The device of claim 19, wherein the media processing instruction includes at least one of play, pause, fast forward, reverse, and stop.

21. The device of claim 20, wherein the media processing instruction is delivered to the first process from a third process.

22. The device of claim 16, wherein the timing synchronization message includes at least one time stamp associated with the first timing information derived from the first timing source.

23. The device of claim 16, wherein the timing synchronization message includes at least one of a time stamp from a base clock of the first timing source, a time stamp from a base clock of the second timing source, a time stamp from a time base associated with the first process, a rate associated with the time base, and a rate scaler between the first and second timing sources.

24. The device of claim 16, wherein the shadow timing information is derived from the second timing source.

25. The device of claim 24, wherein the second timing source includes a common reference clock.

26. The device of claim 16, wherein the first timing information comprises at least one of a base clock of the first timing source and a first movie time base derived from the base clock of the first timing source.

27. The device of claim 26, wherein the shadow timing information comprises at least one of a first shadow time base estimating the base clock of the first timing source and a second shadow time base estimating the first movie time base.

28. The device of claim 27, wherein the first shadow time base and the second shadow time base continuously estimate the base clock of the first timing source and the first movie time base respectively.

29. The device of claim 16, wherein the first timing source includes an audio clock.

30. The p device of claim 16, wherein the processor is further configured to synchronize the second process with the first process by updating the shadow timing information based at least in part on the received synchronization messages.

31. A method for processing media comprising:

processing the media using a first process, wherein the first process accesses a first timing source and a second timing source, and wherein the first process processes media based at least in part on first timing information derived from the first timing source;

processing the media using a second process, wherein the second process accesses the second timing source but cannot access the first timing source, and wherein the second process processes media based at least in part on shadow timing information;

synchronizing the second process with the first process using one or more synchronization messages, generated based at least in part on the first timing source and the second timing source; and

wherein the shadow timing information is an estimate of the first timing information maintained by the second process.

32. The method of claim 31 comprising sending each synchronization message periodically.

33. The method of claim 31 comprising sending each synchronization message in response to an event.

34. The method of claim 33, wherein the event includes receiving, by the first process, a media processing instruction.

35. The method of claim 34, wherein the media processing instruction includes at least one of play, pause, fast forward, reverse, and stop.

36. The method of claim 35 comprising delivering the media processing instruction to the first process from a third process.

37. The method of claim 31, wherein the timing synchronization message includes at least one time stamp associated with the first timing information derived from the first timing source.

38. The method of claim 31, wherein the timing synchronization message includes at least one of time stamp from a base clock of the first timing source, a time stamp from a base clock of the second timing source, a time stamp from a time base associated with the first process, a rate associated with the time base, and a rate scaler between the first and second timing sources.

39. The method of claim 31, wherein the shadow timing information is derived from the second timing source.

40. The method of claim 39, wherein the second timing source includes a common reference clock.

41. The method of claim 31, wherein the first timing information comprises at least one of a base clock of the first timing source and a first movie time base derived from the base clock of the first timing source.

42. The method of claim 41, wherein the shadow timing information comprises at least one of a first shadow time base estimating the base clock of the first timing source and a second shadow time base estimating the first movie time base.

43. The method of claim 42, wherein the first shadow time base and the second shadow time base continuously estimate the base clock of the first timing source and the first movie time base respectively.

44. The method of claim 31, wherein the first timing source includes an audio clock.

45. The method of claim 31, further comprising synchronizing the second process with the first process by updating the shadow timing information based at least in part on the received synchronization messages.

46. A non-transitory computer readable medium having computer executable code embedded therein for processing media, the executable code performing the following functions:

processing the media using a first process, wherein the first process accesses a first timing source and a second timing source, and wherein the first process processes media based at least in part on first timing information derived from the first timing source;

processing the media using a second process, wherein the second process accesses the second timing source but cannot access the first timing source, and wherein the second process processes media based at least in part on shadow timing information;

synchronizing the second process with the first process using one or more synchronization messages, generated based at least in part on the first timing source and the second timing source; and

wherein the shadow timing information is an estimate of the first timing information maintained by the second process.