Time synchronization of multiple time-based data streams with independent clocks

• US 7,765,315 B2
• Filed: 01/08/2007
• Issued: 07/27/2010
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Flick, Christopher L., Bushell, John S., Chapman, Gregory R., Batson, James D.
• Primary Examiner(s): Nguyen; Thu
• Assistant Examiner(s): DOAN, DUYEN MY
• Application Number:
  US11/651,354
• Publication Number:
  US 20080168294A1
• Time in Patent Office: 1,296 Days
• Field of Search: 709/248, 713400-401, 713500-503, 348512-515
• US Class Current: 709/231
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators
• CPC Class Codes: H04N 21/2368 Multiplexing of audio and video streams
• CPC Class Codes: H04N 21/4341 Demultiplexing of audio and video streams
• CPC Class Codes: H04N 21/8547 involving timestamps for synchronizing content

Abstract

Techniques are described for synchronizing multiple time-based data streams with independent clocks wherein relationships between clock rates of timing devices associated with the time-based data streams are determined, and based on these relationships, times in at least one of the time-based data streams may be translated to times in any of the other time-based data streams despite the data streams having independent clocks.

Claims

1. A computer-implemented method for relating time-based data, the computer-implemented method comprising:

allowing a clock rate of a first timing device and a clock rate of a common reference to run at rates that change independently over time;

while continuing to allow the clock rate of the first timing device and the clock rate of the common reference to run at rates that change independently over time, performing the steps of;

ascertaining a first relationship between the clock rate of the first timing device and the clock rate of the common reference;

ascertaining a second relationship between a clock rate of a second timing device and the clock rate of the common reference; and

based on the first relationship and the second relationship, calculating a third relationship between (a) a first set of time-based data that is based on the first timing device and (b) a second set of time-based data that is based on the second timing device; and

wherein the first timing device and the second timing device are two different timing devices;

wherein the clock rates of the first and second timing devices are independent of and different from each other; and

wherein the clock rates of the first and second timing devices are independent of and different from each other; and

wherein the method is implemented by one or more computing devices.

2. The method of claim 1 wherein the common reference is a CPU clock.

3. The method of claim 1 wherein:

the step of calculating a third relationship is based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

further comprising the step of;

based on the third relationship, translating at least one time stamp in the first time base to at least one time stamp in the second time base.

4. The method of claim 1 wherein:

the step of calculating a third relationship is based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

further comprising the step of;

based on the third relationship, translating at least one time duration in the first time base to at least one time duration in the second time base.

5. The method of claim 1 wherein the first and second set of time-based data each comprise time-based data streams, each with at least one time base rooted in separate timing devices, and wherein:

the step of calculating a third relationship is based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

further comprising the step of;

based on the third relationship, synchronizing the time-based data streams.

6. The method of claim 1 wherein the first timing device, the second timing device, and the common reference are connected by a network.

7. The method of claim 1 wherein the common reference is a third timing device that is separate from the first timing device and the second timing device.

8. The method of claim 1 further comprising the step of receiving input designating the common reference.

10. The method of claim 1, further comprising:

based on the third relationship, synchronizing the first set of time-based data in a first time base with the second set of time-based data in a second time base.

11. The method of claim 1, further comprising:

based on the third relationship, calculating a relative rate between a first time base and a second time base; and

resampling the first set of time-based data in the first time base to play the first set of time-based data in synchronization with playing the second set of time-based data in the second time base.

9. A method comprising:

allowing a clock rate of a first timing device and a clock rate of a common timing device to run at rates that change independently over time;

while continuing to allow the clock rate of the first timing device and the clock rate of the common timing device to run at rates that change independently over time, performing the steps of;

calculating a first rate scaler between the clock rate of the first timing device and the clock rate of the common timing device;

calculating a second rate scaler between a clock rate of a second timing device and the clock rate of the common timing device; and

translating a time in a first time base running at a first rate and rooted in the first timing device to a time in a second time base running at a second rate and rooted in the second timing device, wherein the step of translating comprises analyzing at least;

(a) the first rate scaler, (b) the second rate scaler, (c) the time in the first time base, (d) a pair of times each different from (c), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device;

(e) the rate associated with the first time base, and (f) the rate associated with the second time base; and

wherein the first timing device and the second timing device are two different timing devices;

wherein the method is implemented by one or more computing devices.

12. A machine-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform:

allowing a clock rate of a first timing device and a clock rate of a common reference to run at rates that change independently over time;

while continuing to allow the clock rate of the first timing device and the clock rate of the common reference to run at rates that change independently over time, performing the steps of;

ascertaining a first relationship between the clock rate of the first timing device and the clock rate of the common reference;

ascertaining a second relationship between a clock rate of a second timing device and the clock rate of the common reference; and

based on the first relationship and the second relationship, calculating a third relationship between (a) a first set of time-based data that is based on the first timing device and (b) a second set of time-based data that is based on the second timing device; and

wherein the first timing device and the second timing device are two different timing devices;

wherein the clock rates of the first and second timing devices are independent of and different from each other.

13. The medium of claim 12 wherein the common reference is a CPU clock.

14. The medium of claim 12 wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform:

calculating the third relationship based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

based on the third relationship, translating at least one time stamp in the first time base to at least one time stamp in the second time base.

15. The medium of claim 12 wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform:

calculating the third relationship based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

based on the third relationship, translating at least one time duration in the first time base to at least one time duration in the second time base.

16. The medium of claim 12 wherein the first and second set of time-based data each comprise time-based data streams, each with at least one time base rooted in separate timing devices, and wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform:

calculating the third relationship based on at least;

(a) one time in a first time base associated with the first set of time-based data and based on the first timing device, (b) one time in a second time base associated with the second set of time-based data and based on the second timing device, (c) a pair of times different from (a) or (b), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device; and

(d) a rate associated with the first time base; and

based on the third relationship, synchronizing the time-based data streams.

17. The medium of claim 12 wherein the first timing device, the second timing device, and the common reference are connected by a network.

18. The medium of claim 12 wherein the common reference is a third timing device that is separate from the first timing device and the second timing device.

19. The medium of claim 12 wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform receiving input designating the common reference.

20. The medium of claim 12 the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform:

based on the third relationship, synchronizing the first set of time-based data in a first time base with the second set of time-based data in a second time base.

21. The medium of claim 12, wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, causes the one or more processors to perform:

based on the third relationship, calculating a relative rate between a first time base and a second time base; and

resampling the first set of time-based data in the first time base to play the first set of time-based data in synchronization with playing the second set of time-based data in the second time base.

22. A machine-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform:

allowing a clock rate of a first timing device and a clock rate of a common timing device to run at rates that change independently over time;

while continuing to allow the clock rate of the first timing device and the clock rate of the common timing device to run at rates that change independently over time, performing the steps of;

calculating a first rate scaler between the clock rate of the first timing device and the clock rate of the common timing device;

calculating a second rate scaler between a clock rate of a second timing device and the clock rate of the common timing device; and

translating a time in a first time base running at a first rate and rooted in the first timing device to a time in a second time base running at a second rate and rooted in the second timing device, wherein the step of translating comprises analyzing at least;

(a) the first rate scaler, (b) the second rate scaler, (c) the time in the first time base, (d) a pair of times each different from (c), measured at the same time, one of the pair of times based on the first time base and the other of the pair of times based on the first timing device;

(e) the rate associated with the first time base, and (f) the rate associated with the second time base; and

wherein the first timing device and the second timing device are two different timing devices.