System for synchronization by modifying the rate of conversion by difference of rate between first clock and audio clock during a second time period

• US 5,875,354 A
• Filed: 03/01/1996
• Issued: 02/23/1999
• Est. Priority Date: 03/01/1996
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Charlton, Paul, Gurganus, Keith
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): Chen, Anderson I.
• Application Number:
  US08/609,395
• Time in Patent Office: 1,089 Days
• Field of Search: 395/806, 395/551, 395/881, 395/553
• US Class Current: 710/61
• CPC Class Codes: G06F 2205/061 Adapt frequency, i.e. clock frequency at one side is adapted to clock frequency, or average clock frequency, at the other side; Not pulse stuffing only
• CPC Class Codes: G06F 5/06 for changing the speed of data flow, i.e. speed regularising or timing, e.g. delay lines, FIFO buffers; over- or underrun control therefor G06F7/78 takes precedence

Abstract

A method and apparatus for synchronizing the presentation of time dependent data to a first dock having a first frequency is disclosed. First, a rate conversion is performed on a data stream for a first time period. Second, the rate of conversion is modified to provide a modified rate of conversion. Third, a rate of conversion having a modified rate of conversion is performed on the data stream for a second time period. The second and third steps are repeated until all samples in the data stream are presented. The rate of conversion is modified from one period to the next based on a measurement of the difference between a rate for the first clock and the rate of a second less precise clock.

Claims

1. A method for synchronizing a presentation of a data stream to a first clock having a first frequency, said data stream having a plurality of data values, said method comprising the steps of:

a) performing a rate conversion on said data stream during a first time period, said rate conversion being a first predetermined rate of conversion;

b) modifying the first predetermined rate of conversion to provide a modified rate of conversion for said synchronizing of the presentation of said data stream, wherein said first determined rate of conversion is modified based on a measurement of a difference between a rate of said first clock having a first frequency and a rate of a second clock having a second frequency, wherein said second clock is an audio clock of an audio subsystem; and

c) performing a rate conversion with the modified rate of conversion on the data stream for a second time period.

2. The method for synchronizing the presentation of a data stream as set forth in claim 1, further comprising the step of repeating the step of modifying the first predetermined rate of conversion to provide a modified rate of conversion and the step of performing the rate conversion with the modified rate of conversion until all data values in the data stream are processed.

3. The method for synchronizing the presentation of a data stream as set forth in claim 1, wherein said first clock is a real time clock of a computer system.

4. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a network port, said network port providing audio information.

5. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a network port, said network port providing video information.

6. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a network port, said network port providing audio and video information.

7. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a network port, said network port providing a shared environment.

8. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a storage medium, said storage medium providing audio information.

9. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a storage medium, said storage medium providing video information.

10. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a storage medium, said storage medium providing audio and video information.

11. The method of synchronizing a data stream as set forth in claim 2, wherein the data stream is received from a storage medium, said storage medium providing a plurality of different media.

12. An apparatus for synchronizing the presentation of a data stream to a first clock having a first frequency, said data stream having a plurality of samples, said apparatus comprising:

a) a first logic circuit having an input for receiving a data stream, said first logic circuit for performing rate conversion on the data stream at a first rate of conversion for a first period of time;

b) a digital to analog conversion circuit, coupled to the first logic circuit, for converting the samples into analog waveforms at a second rate of conversion; and

c) a second logic circuit, coupled to a first clock having a first frequency, the digital to analog converter and the first logic circuit, said second logic circuit receiving a first value from the digital to analog converter, said value representing the number of samples played through the conversion circuit at any given time and based on the first value modifying the rate of conversion to provide a modified rate of conversion, wherein said rate of conversion is modified based on a measurement of a difference between a rate for the first clock having a first frequency and a rate of a second clock having a second frequency, wherein said second clock is an audio clock of an audio subsystem.

13. The apparatus for synchronizing the presentation of a data stream as set forth in claim 12, wherein the first logic circuit performs the rate of conversion on the data stream for a second period of time using the modified rate of conversion.

14. The apparatus for synchronizing the presentation of a data stream as set forth in claim 12, wherein the first clock is a real time clock of a computer system.

15. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a network port, said network port providing audio information.

16. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a network port, said network port providing video information.

17. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a network port, said network port providing audio and video information.

18. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a network port, said network port providing a shared environment.

19. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a storage medium, said storage medium providing audio information.

20. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a storage medium, said storage medium providing video information.

21. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a storage medium, said storage medium providing audio and video information.

22. An apparatus for synchronizing a data stream as set forth in claim 13, wherein the data stream is received from a storage medium, said storage medium providing a plurality of different media.

23. An apparatus for synchronizing the presentation of a data stream, said data stream having a plurality of samples, said apparatus comprising:

a) first logic circuit having an input for receiving the data stream, said first logic circuit for performing rate conversion on the data stream at a first rate of conversion for a first period of time;

b) a data buffer, coupled to the first logic circuit, for storing data values;

c) a conversion circuit, coupled to the data buffer for converting the samples into analog waveforms at a second rate of conversion; and

d) a second logic circuit, coupled to a first clock having a first frequency and the data buffer, and the first logic circuit, said second logic circuit receiving a first value representing the number of samples stored in the data buffer at any given time and based on the first value modifying the rate of conversion of the first logic circuit to provide a modified rate of conversion to the first logic circuit, wherein said rate of conversion is modified based on a measurement of a difference between a rate for the first clock having a first frequency and a rate of a second clock having a second frequency, wherein said second clock of a second frequency is an audio clock of an audio subsystem.

24. The apparatus for synchronizing the presentation of a data stream as set forth in claim 23, wherein the first logic circuit performs the rate of conversion on the data stream for a second period of time using the modified rate of conversion.

25. The apparatus for synchronizing the presentation of a data stream as set forth in claim 23, wherein the clock having the first frequency is a real time clock of a computer system.

26. In a computer system having a digital media source connected with a digital media presentation device, the digital media source and the digital media presentation device each having a first and second clock, a method for synchronizing the presentation of a data stream sent by the digital media source to the digital media presentation device comprising the steps of:

a) said digital media presentation device receiving the stream of data;

b) synchronizing the first clocks of the digital media source and the digital media presentation device via a synchronization protocol;

c) synchronizing the presentation of the data using the second clock of the digital media presentation device to the first clock of the digital media presentation device by performing the following

i) performing a rate conversion of said data stream for a first period of time, said rate conversion having a first rate of conversion;

ii) modifying the first rate of conversion to provide a modified rate of conversion, wherein said rate of conversion is modified based on a measurement of a difference between a rate for the first clock having a first frequency and a rate of the second clock having a second frequency, wherein said second clock of a second frequency is an audio clock of an audio subsystem in the workstation; and

iii) performing a rate conversion on said data stream with the modified rate of conversion for a second period of time.

27. The method for synchronizing the presentation of a data stream as set forth in claim 26, further comprising the step of repeating the step of modifying the first predetermined rate of conversion to provide a modified rate of conversion and the step of performing the rate conversion with the modified rate of conversion until all data values in the data stream are processed.

28. The method of synchronizing the presentation of a data stream as set forth in claim 26, wherein the clock having the first frequency is a real time clock of the workstation.

29. The method of synchronizing a data stream as set forth in claim 26, wherein the data stream represents audio information.

30. The method of synchronizing a data stream as set forth in claim 26, wherein the data stream comprises video information.

31. The method of synchronizing a data stream as set forth in claim 26, wherein the data stream comprises video and audio information.

32. An apparatus for synchronizing the presentation of a data stream, said data stream having a plurality of samples, said apparatus comprising:

a) first logic circuit having an input for receiving a data stream, said first logic circuit for performing rate conversion on the data stream at a first rate of conversion for a first period of time;

b) a conversion means, coupled to the first logic means for converting the samples into analog waveforms at a second rate of conversion; and

c) a second logic means coupled to a first clock having a first frequency and the first logic means, said second logic means having an input for receiving a first value, said first value representing the number of samples played through the conversion means at any given time and based on the first value modifying the rate of conversion to provide a modified rate of conversion, wherein said rate of conversion is modified based on a measurement of a difference between a rate for the first clock having a first frequency and a rate of a second clock having a second frequency, wherein said second clock is an audio clock of an audio subsystem.

33. The apparatus for synchronizing the presentation of a data stream, as set forth in claim 32, wherein the first logic means performs the rate of conversion on the data stream for a second period of time using the modified rate of conversion.

34. The apparatus for synchronizing the presentation of a data stream, as set forth in claim 32, wherein the first clock is a real time clock of a computer system.

35. An apparatus for synchronizing the presentation of a media steam, said media stream having a plurality of media samples, to a first clock rate, said apparatus comprising:

a rate conversion unit for receiving a media stream and performing rate conversion on the media stream for a first period of time;

a presentation unit, coupled to the rate conversion unit, said presentation unit including a first input for receiving a second clock rate, said presentation unit presenting the media to an observer;

a rate modification unit, coupled to the rate conversion unit and the presentation unit, said rate modification unit including a first input for receiving a sample count from the presentation unit, said sample count representing the number of samples presented to the observer, and a second input for receiving the first clock rate, said rate modification unit, in response to the sample count and the first clock rate, generating a modified second clock rate and providing the modified second clock rate to the rate conversion unit, wherein said second clock rate is for an audio subsystem.

36. The apparatus as set forth in claim 35 wherein the rate conversion unit, upon receipt of the modified second clock rate, performs rate conversion on the media stream for a second period of time with the modified second clock rate.

37. The apparatus as set forth in claim 35 wherein the media stream includes a plurality of media type with each media type having its own rate conversion unit, presentation unit, and rate modification unit;

and

wherein the rate modification of each media includes an input for receiving the first clock rate and the presentation unit of each media includes an input for receiving the second clock rate.

38. The apparatus as set forth in claim 37 wherein the second clock rate of each presentation unit of each media is different.

39. The apparatus as set forth in claim 38 wherein the first clock rate for each rate modification unit for each media is the same time reference.