SYNCHRONIZING DIGITAL AUDIO AND ANALOG VIDEO FROM A PORTABLE MEDIA DEVICE

• US 20090060446A1
• Filed: 06/13/2008
• Published: 03/05/2009
• Est. Priority Date: 09/04/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Holden, Paul, Girish, Muthya
• Granted Patent: US 9,467,735 B2
• Time in Patent Office: Days
• US Class Current: 386/356
• CPC Class Codes: H04N 21/2368 Multiplexing of audio and video streams
• CPC Class Codes: H04N 21/4126 The peripheral being portable, e.g. PDAs or mobile phones
• CPC Class Codes: H04N 21/4135 external recorder interface circuits between an apparatus for recording television signals and a television receiver H04N5/775
• CPC Class Codes: H04N 21/43076 of the same content streams on multiple devices, e.g. when family members are watching the same movie on different devices
• CPC Class Codes: H04N 21/4341 Demultiplexing of audio and video streams
• CPC Class Codes: H04N 21/436 Interfacing a local distribution network, e.g. communicating with another STB or one or more peripheral devices inside the home
• CPC Class Codes: H04N 21/8106 involving special audio data, e.g. different tracks for different languages
• CPC Class Codes: H04N 5/765 Interface circuits between an apparatus for recording and another apparatus
• CPC Class Codes: H04N 5/85 on discs or drums
• CPC Class Codes: H04N 5/907 using static stores, e.g. storage tubes or semiconductor memories H04N5/91 takes precedence
• CPC Class Codes: H04N 9/8205 involving the multiplexing of an additional signal and the colour video signal

Abstract

A portable media device (PMD) can produce an isochronous audio/video experience when the PMD provides a digital audio signal to the accessory while displaying analog video on an accessory-independent display. The accessory can communicate audio latency information to the PMD. The PMD can delay a video portion of a presentation, relative to providing the digital audio signal to the accessory, based on the audio latency information communicated by the accessory. As a result, the user may perceive an isochronous presentation of the audio and video portions of the presentation.

Claims

1. A method of presenting an audio/video track using a portable media device and an accessory device, the method comprising, by the portable media device:

receiving from the accessory device audio latency information;

determining a video delay time based on the audio latency information;

sending digital audio data to the accessory, the digital audio data corresponding to an audio portion of the audio/video track; and

providing an analog video signal to a video display, the analog video signal corresponding to a video portion of the audio/video track,

wherein the analog video signal is delayed, relative to the digital audio signal, by the video delay time.

2. The method of claim 1 wherein the video display is a component of the portable media device.

3. The method of claim 1 further comprising:

sending to the accessory sample rate information indicating a sample rate to be used for providing the digital audio data.

4. The method of claim 3 wherein the accessory sends the audio latency information in response to the sample rate information.

5. The method of claim 1, wherein the audio latency information is received via a serial interface.

6. The method of claim 1, wherein the digital audio data is sent to the accessory using a Universal Serial Bus (“

USB”

) audio protocol.

7. A method of presenting an audio/video track using a portable media device and an accessory device, the method comprising, by the accessory device:

receiving from the portable media device a first sample rate for digital audio data corresponding to an audio portion of a first audio/video track;

determining, based at least in part on the first sample rate, an audio latency parameter value;

sending the audio latency parameter value to the portable media device, wherein the portable media device uses the audio latency parameter to determine a delay time for a video portion of the first audio/video track;

receiving the digital audio data corresponding to the audio portion of the first audio/video track from the portable media device;

processing the digital audio data to produce an analog audio signal, wherein processing of the digital audio data occurs with a latency corresponding to the audio latency parameter value; and

delivering the analog audio signal to a speaker.

8. The method of claim 7 wherein determining the audio latency parameter value includes accessing a stored audio latency parameter value.

9. The method of claim 7 wherein determining the audio latency parameter value includes selecting a stored audio latency parameter value from a group of stored audio latency parameter values, wherein the selection is based at least in part on the first sample rate.

10. The method of claim 7 wherein the group of stored audio latency parameter values includes values determined from measurements of the propagation of digital audio signals having a number of different sample rates through the accessory device.

11. The method of claim 7, wherein the group of stored audio latency parameter values includes values determined from calculations of the propagation of digital audio signals having a number of different sample rates through the accessory device.

12. The method of claim 7 further comprising:

receiving from the portable media device a second sample rate for digital audio data corresponding to an audio portion of a second audio/video track;

determining, based at least in part on the second sample rate, an updated audio latency parameter value;

sending the updated audio latency parameter value to the portable media device, wherein the portable media device uses the updated audio latency parameter to determine a delay time for a video portion of the second audio/video track;

receiving the digital audio data corresponding to the audio portion of the second audio/video track from the portable media device;

processing the digital audio data to produce an analog audio signal, wherein processing of the digital audio data occurs with a latency corresponding to the updated audio latency parameter value; and

delivering the analog audio signal to a speaker.

13. The method of claim 7 wherein the audio latency parameter value is sent via a serial interface.

14. The method of claim 7 wherein the digital audio data is received from the portable media device using a Universal Serial Bus (“

USB”

) audio protocol.

15. The method of claim 7 further comprising, by the accessory:

during receiving of the digital audio data, detecting a change to an audio processing setting of the accessory device;

determining, based in part on the audio processing setting, an updated audio latency parameter value; and

sending the updated audio latency parameter value to the portable media device, wherein the portable media device uses the updated audio latency parameter to determine a new delay time for the video portion of the first audio/video track.

16. The method of claim 15 wherein the audio processing setting is an equalizer setting.

17. A method of synchronizing a video presentation on a portable media device with a corresponding audio presentation on an accessory device, the method comprising:

determining an audio latency characteristic for a digital audio signal propagating through the accessory device;

storing audio latency information corresponding to the audio latency characteristic in the accessory device;

coupling the portable media device to the accessory device; and

providing the audio latency information from the accessory device to the portable media device.

18. The method of claim 17 wherein the audio latency characteristic is an amount of time elapsed between the accessory device receiving a digital audio signal and the accessory device producing sound corresponding to the digital audio signal.

19. The method of claim 17 further comprising:

delivering digital audio data for the audio presentation from the portable media device to the accessory device; and

delaying, within the portable media, device, delivery of the video presentation by an amount of time determined from the audio latency information.

20. The method of claim 19 wherein the delivering the audio presentation includes transferring a sequence of data packets according to a digital audio protocol.

21. The method of claim 20 wherein the digital audio protocol is a Universal Serial Bus (“

USB”

) audio protocol.

22. A method of synchronizing a video presentation on a portable media device with a corresponding audio presentation on an audio accessory device, the method comprising:

coupling the portable mobile device to the audio accessory device;

sending, from the audio accessory device to the portable media device, a command providing an audio latency parameter for the audio accessory device;

providing digital audio data for the audio presentation from the portable media device to the audio accessory device; and

delaying presentation of the video presentation by an amount of time determined from the audio latency parameter.

23. An accessory for use with a portable media device, the accessory comprising:

an audio processing path configured to produce an analog audio signal from a digital audio signal;

an interface configured to communicate with a portable media device, the interface being configured to receive a digital audio signal from the portable media device and further configured to exchange with the portable media device commands and information related to the presentation of digital audio data; and

a controller coupled to the interface and to the audio processing path, the controller being configured to;

send a first command to the portable media device via the interface, the first command providing to the portable media device audio latency information corresponding to a latency characteristic of the audio processing path;

receive digital audio data from the portable media device via the interface; and

deliver the digital audio data to the audio processing path.

24. The accessory of claim 23 wherein the audio latency information is usable by the portable media device to determine a delay time for delaying a video presentation corresponding to the digital audio data received by the accessory such that the video presentation is isochronous with presentation of the analog audio signal produced by the audio processing path of the accessory.

25. The accessory of claim 23 wherein the controller is further configured to receive a second command from the portable media device via the interface, the second command including a sample rate for digital audio data to be received from the portable media device.

26. The accessory of claim 25 wherein the controller is further configured to send the second command in response to the first command.

27. The accessory of claim 26 wherein the controller is further configured to select the audio latency information to be sent based at least in part on the sample rate.

28. The accessory of claim 23 wherein the audio processing path includes an input buffer and the audio latency information includes buffer latency information corresponding to a latency associated with the input buffer.

29. The accessory of claim 23 wherein the audio processing path includes an equalizer section and the audio latency information depends at least in part on a latency associated with the equalizer section.

30. The accessory of claim 23 wherein the audio latency information depends at least in part on a sample rate of the digital audio data.

31. The accessory of claim 23 wherein the interface is configured to receive digital audio data according to a Universal Serial Bus (“

USB”

) audio protocol.

32. A portable media device for use with an accessory, the portable media device comprising:

a video path configured to produce an analog video signal;

an interface configured to communicate with an accessory, the interface being configured to send a digital audio signal to the accessory and further configured to exchange with the accessory device commands and information related to the presentation of digital audio data; and

a processor coupled to the interface and to the video path, the processor being configured to;

receive a first command from the accessory via the interface, the first command providing to the portable media device audio latency information corresponding to a latency characteristic of the accessory;

determine a video delay time for a video portion of an audio/video track based on the audio latency information;

send digital audio data for an audio portion of the audio/video track to the accessory via the interface; and

deliver the video portion of the audio/video track to the video path, wherein the delivery of the video portion is delayed, relative to sending the digital audio data to the accessory, by the video delay time.

33. The portable media device of claim 32 wherein the processor is further configured to send a second command to the accessory via the interface, the second command including a sample rate for digital audio data to be sent by the portable media device.

34. The portable media device of claim 33 wherein the first command is received in response to sending the second command.

35. The portable media device of claim 32 wherein the interface is configured to send digital audio data according to a Universal Serial Bus (“

USB”

) audio protocol.