METHODS AND APPARATUS FOR SYNCHRONIZATION OF MEDIA PLAYBACK WITHIN A WIRELESS NETWORK

• US 20160142988A1
• Filed: 11/19/2014
• Published: 05/19/2016
• Est. Priority Date: 11/19/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Powell, Richard, Naito, Daniel, Hollabaugh, James, Klingler, Dan
• Granted Patent: US 10,085,224 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04R 2420/07 Applications of wireless loudspeakers or wireless microphones
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Methods and apparatus for synchronization of media playback within a wireless network. In one embodiment, the present disclosure is directed to precision synchronization over time, based on repeated measurements of a common time reference. In one exemplary embodiment, the common time reference is a Time Synchronization Function (TSF) of a Wireless Local Area Network (WLAN). In another exemplary embodiment of the present disclosure, the application processor and the modem processor measure a pulse width and the aforementioned common time reference in order to adjust media playback.

Claims

1. A method for precisely synchronizing media processing within a network, the method comprising:

receiving a common time stamp of a common time reference;

receiving media data associated with the common time reference;

deriving a local version of the common time reference for media playback based on the common time stamp; and

playing the media in accordance with the derived time reference.

2. The method of claim 1, where the network comprises a wireless local area network (WLAN) and the common time reference comprises a time synchronization function (TSF) value received via a beacon.

3. The method of claim 2, where the local version of the common time reference is clocked from a free running clock oscillator.

4. The method of claim 3, where deriving the local version of the common time reference comprises determining a rate mismatch between the local version of the common time reference and the common time reference.

5. The method of claim 4, where the determination of rate mismatch is based on an analysis of a plurality of observed time stamps and an ideal timeline derived from the plurality of observed time stamps.

6. A method for interrupt driven time synchronization within a device, the method comprising:

generating a common event between a first and a second processor;

observing a first number of clock cycles of the first processor during the common event;

observing a second number of clock cycles of the second processor during the common event;

determining a rate mismatch based on the first and second number;

correcting one or more media samples for playback on the first processor based on the determined rate mismatch; and

where the one or more media samples are provided by the second processor.

7. The method of claim 6, where the common event comprises a pulse width generated by the first processor setting a latch, and responsively the second processor resetting the latch.

8. The method of claim 7, further comprising receiving one or more time stamps via a main link.

9. The method of claim 8, where the received one or more time stamps are associated with at least one edge of the pulse width.

10. A wireless media device configured to receive media via a wireless network, the wireless media device comprising:

a first and a second processor;

a first clock associated with the first processor and a second clock associated with the second processor; and

a non-transitory computer readable medium comprising one or more instructions which is configured to cause the first processor to, when executed;

request a time synchronization event;

observe a first number of first clock cycles of the first clock during a common event;

receive a second number of second clock cycles of the second clock during the common event; and

determine a rate mismatch based on the first and second number; and

correct one or more media samples for playback based on the determined rate mismatch.

11. The wireless media device of claim 10, where the first and second processor comprise an application processor and a wireless modem.

12. The wireless media device of claim 11, where the one or more instructions are further configured to cause the first processor to, when executed:

set a latch;

where the second processor is configured to responsively reset the latch; and

measure a pulse width generated by the latch.

13. The wireless media device of claim 11, where the media comprises one or more audio data streamed via the wireless network.

14. The wireless media device of claim 11, where the wireless modem is time synchronized to the wireless network.

15. The wireless media device of claim 14, where the one or more instructions are further configured to cause the first processor to, when executed:

receive a time stamp via an out-of-band link with the second processor, the time stamp associated with the common event.

16. The wireless media device of claim 10, where the one or more media samples are streaming audio samples.

17. The wireless media device of claim 10, where the second clock is selected to oscillate at a frequency that is substantially similar to a radio frequency of the wireless network.

18. The wireless media device of claim 17, where the first clock is selected according to one or more processor capabilities.

19. The wireless media device of claim 10, where the received second number of second clock cycles is received via an out-of-band link with the second processor.

20. The wireless media device of claim 10, where the rate mismatch is determined based on historic measurements.