Time Synchronization of Multiple Time-Based Data Streams with Independent Clocks

• US 20100257396A1
• Filed: 06/15/2010
• Published: 10/07/2010
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chapman, Gregory R., Batson, James D., Flick, Christopher L., Bushell, John S.
• Granted Patent: US 8,316,147 B2
• Time in Patent Office: Days
• US Class Current: 713/400
• 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 machine-implemented method, comprising:

determining a first relationship between a clock rate of a first timing device and a clock rate of a reference timing device;

determining a second relationship between a clock rate of a second timing device and the clock rate of the same reference timing device; and

based at least partially upon the first relationship and the second relationship, determining a timing relationship between (a) a first time base that is based on the first timing device and (b) a second time base that is based on the second timing device;

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

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

2. The method of claim 1, further comprising:

based at least partially upon the timing relationship between the first and second time bases, translating a time in the first time base to a corresponding time in the second time base.

3. The method of claim 1, further comprising:

based at least partially upon the timing relationship between the first and second time bases, translating a time duration in the first time base to a corresponding time duration in the second time base.

4. The method of claim 1, wherein a first time-based data stream is associated with the first time base and a second time-based data stream is associated with the second time base, and wherein the method further comprises:

based at least partially upon the timing relationship between the first and second time bases, synchronizing the first and second time-based data streams.

5. The method of claim 1, wherein a first set of time-based data is associated with the first time base and a second set of time-based data is associated with the second time base, and wherein the method further comprises:

based at least partially upon the timing relationship between the first and second time bases, relating a portion of the first set of time-based data associated with a particular time in the first time base with a portion of the second set of time-based data associated with a certain time in the second time base, wherein the certain time in the second time base corresponds to the particular time in the first time base.

6. The method of claim 1, wherein a first set of time-based data is associated with the first time base and a second set of time-based data is associated with the second time base, and wherein the method further comprises:

based at least partially upon the timing relationship between the first and second time bases, calculating a relative rate between the first time base and the second time base; and

sampling the first set of time-based data at a first rate and sampling the second set of time-based data at a second rate such that the first rate relative to the second rate is substantially equal to the relative rate.

7. The method of claim 1, wherein the first timing device is used as a time source for the first time base, and wherein the second timing device is used as a time source for the second time base.

8. The method of claim 1, wherein the reference timing device is a separate timing device from the first timing device and the second timing device.

9. The method of claim 1, wherein the first relationship comprises a first rate scaler between the clock rate of the first timing device and the clock rate of the reference timing device, and wherein the second relationship comprises a second rate scaler between the clock rate of the second timing device and the clock rate of the reference timing device.

10. The method of claim 1, wherein the first relationship comprises a first ratio between the clock rate of the first timing device and the clock rate of the reference timing device, and wherein the second relationship comprises a second ratio between the clock rate of the second timing device and the clock rate of the reference timing device.

11. A machine-readable storage medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform the operations of:

determining a first relationship between a clock rate of a first timing device and a clock rate of a reference timing device;

determining a second relationship between a clock rate of a second timing device and the clock rate of the same reference timing device; and

based at least partially upon the first relationship and the second relationship, determining a timing relationship between (a) a first time base that is based on the first timing device and (b) a second time base that is based on the second timing device;

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

12. The machine-readable storage medium of claim 11, further storing instructions which cause one or more processors to perform the operation of:

based at least partially upon the timing relationship between the first and second time bases, translating a time in the first time base to a corresponding time in the second time base.

13. The machine-readable storage medium of claim 11, further storing instructions which cause one or more processors to perform the operation of:

based at least partially upon the timing relationship between the first and second time bases, translating a time duration in the first time base to a corresponding time duration in the second time base.

14. The machine-readable storage medium of claim 11, wherein a first time-based data stream is associated with the first time base and a second time-based data stream is associated with the second time base, and wherein the machine-readable storage medium further stores instructions which cause one or more processors to perform the operation of:

based at least partially upon the timing relationship between the first and second time bases, synchronizing the first and second time-based data streams.

15. The machine-readable storage medium of claim 11, wherein a first set of time-based data is associated with the first time base and a second set of time-based data is associated with the second time base, and wherein the machine-readable storage medium further stores instructions which cause one or more processors to perform the operation of:

based at least partially upon the timing relationship between the first and second time bases, relating a portion of the first set of time-based data associated with a particular time in the first time base with a portion of the second set of time-based data associated with a certain time in the second time base, wherein the certain time in the second time base corresponds to the particular time in the first time base.

16. The machine-readable storage medium of claim 11, wherein a first set of time-based data is associated with the first time base and a second set of time-based data is associated with the second time base, and wherein the machine-readable storage medium further stores instructions which cause one or more processors to perform the operations of:

based at least partially upon the timing relationship between the first and second time bases, calculating a relative rate between the first time base and the second time base; and

sampling the first set of time-based data at a first rate and sampling the second set of time-based data at a second rate such that the first rate relative to the second rate is substantially equal to the relative rate.

17. The machine-readable storage medium of claim 11, wherein the first timing device is used as a time source for the first time base, and wherein the second timing device is used as a time source for the second time base.

18. The machine-readable storage medium of claim 11, wherein the reference timing device is a separate timing device from the first timing device and the second timing device.

19. The machine-readable storage medium of claim 11, wherein the first relationship comprises a first rate scaler between the clock rate of the first timing device and the clock rate of the reference timing device, and wherein the second relationship comprises a second rate scaler between the clock rate of the second timing device and the clock rate of the reference timing device.

20. The machine-readable storage medium of claim 11, wherein the first relationship comprises a first ratio between the clock rate of the first timing device and the clock rate of the reference timing device, and wherein the second relationship comprises a second ratio between the clock rate of the second timing device and the clock rate of the reference timing device.