System and method for synchronizing playback of audio and video

• US 20080187282A1
• Filed: 02/05/2007
• Published: 08/07/2008
• Est. Priority Date: 02/05/2007
• Status: Active Grant

• Current Assignee: Thales Avionics Incorporated (Thales SA)
• Original Assignee: Thales Avionics Incorporated (Thales SA)
• Inventors: Treneer, George, Norton, Lyle K., Brady, Kenneth A.
• Granted Patent: US 8,027,560 B2
• Time in Patent Office: Days
• US Class Current: 386/66
• CPC Class Codes: H04L 65/4015 where at least one of the additional parallel sessions is real time or time sensitive, e.g. white board sharing, collaboration or spawning of a subconference
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04L 67/12 specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
• CPC Class Codes: H04N 21/2146 located in mass transportation means, e.g. aircraft, train or bus flight-deck installations for entertainment or communications B64D11/0015; arrangements specially adapted for transportation systems in broadcast systems H04H20/62; moving wireless networks H04W84/005
• 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 21/47202 for requesting content on demand, e.g. video on demand
• CPC Class Codes: H04N 21/64322 IP
• CPC Class Codes: H04N 5/073 for mutually locking plural sources of synchronising signals, e.g. studios or relay stations
• CPC Class Codes: H04N 5/775 between a recording apparatus and a television receiver
• CPC Class Codes: H04N 7/52 Systems for transmission of a pulse code modulated video signal with one or more other pulse code modulated signals, e.g. an audio signal or a synchronizing signal assembling of a multiplex stream by combining a video stream with other content or additional data, remultiplexing of multiplex streams, insertion of stuffing bits into the multiplex stream, assembling of a packetised elementary stream at server side H04N21/236; disassembling of a multiplex stream, remultiplexing of multiplex streams, extraction or processing of Service Information, disassembling of packetised elementary stream at client side H04N21/434
• CPC Class Codes: H04N 9/8042 involving data reduction
• CPC Class Codes: H04N 9/8063 using time division multiplex of the PCM audio and PCM video signals

Abstract

A system and method for providing a digital In-Flight Entertainment (IFE) system in a vehicle, such as an aircraft, that is capable of presenting a video program and associated audio in a synchronized manner to a large number of individual video monitors and speakers. The system and method employ processing operations in at least one decoder of the IFE system, to perform operations such as adjusting a local clock based on a master clock, setting a delay time in relation to a master clock, and adjusting video and audio playback based on the delay, to substantially synchronize playback of the audio and video data by the audio and video players, to thus eliminate or at least minimize the negative effects of source and load based jitter, network delays, clock drifts, network errors and decoder buffering differences, on synchronizing video and audio playback.

Claims

1. A method for synchronizing digital video and audio playback by at least one video player and at least one audio player in a system, the method comprising:

providing digital video and audio data to at least one decoder associated with the video and audio player; and

operating the decoder to adjust a local clock based on a master clock derived from content of the data, set a delay time in relation to the master clock, and adjust video and audio playback based on the delay, to substantially synchronize playback of the audio and video data by the audio and video players.

2. A method as claimed in claim 1, wherein the step of operating the decoder to adjust the local clock comprises:

initializing the local clock upon receipt of a program clock reference (PCR); and

upon receipt of a subsequent PCR, determining whether to adjust the local clock based on a value of the local clock in relation to a presentation time stamp (PTS).

3. A method as claimed in claim 2, wherein the step of operating the decoder to adjust the local clock further comprises:

adjusting the value of the local clock to substantially match the PTS if the value of the local clock is greater than the PTS.

4. A method as claimed in claim 1, wherein the step of operating the decoder to adjust video and audio playback in relation to the master clock comprises:

establishing the delay time; and

setting playback times of the audio and video players such that upon receipt of the audio and video data, the audio and video players refrain from playing back the audio and video data for a time equal to the delay time.

5. A method as claimed in claim 1, wherein the step of operating the decoder to adjust video playback comprises:

comparing a time value at which a video frame is being presented by the video player in relation to a sum of a time of the master clock and the delay time; and

operating the video player to restart, or to replay or skip the video frame, based on the comparison.

6. A method as claimed in claim 5, comprising:

operating the video player to restart video presentation when the time value is greater than the sum by a first amount.

7. A method as claimed in claim 6, comprising:

operating the video player to skip presenting the video frame when the time value is greater than the sum by a second amount that is less than the first amount.

8. A method as claimed in claim 6, comprising:

operating the video player to repeat presenting the video frame when the time value is less than the sum by a third amount that is less than the first amount.

9. A method as claimed in claim 1, wherein the step of operating the decoder to adjust audio playback comprises:

comparing a time value at which a moment of audio is being presented by the audio player in relation to a sum of a time of the master clock and the delay time; and

operating the audio player to restart, skip ahead in the audio or refrain from presenting audio for a period, based on the comparison.

10. A method as claimed in claim 9, comprising:

operating the audio player to restart audio presentation when the time value is greater than the sum by a first amount.

11. A method as claimed in claim 10, comprising:

operating the audio player to refrain from presenting audio for the period, when the time value is greater than the sum by a second amount that is less than the first amount.

12. A method as claimed in claim 10, comprising:

operating the audio player to skip ahead in the audio when the time value is less than the sum by a third amount that is less than the first amount.

13. A method as claimed in claim 1, further comprising:

adjusting a frequency of at least one of a playback clock associated with the video player and a playback clock associated with the audio player, in relation to a clock associated with a source that provides the digital and audio data.

14. A method as claimed in claim 1, wherein:

the system comprises a plurality of video and audio players; and

the providing step provides the digital and audio data to a plurality of decoders associated with the video and audio players; and

the operating step operates each of the decoders to adjust its local clock based on the master clock, set the delay time in relation to the master clock, and adjust video and audio playback based on the delay, to substantially synchronize playback of the audio and video data by its respective audio and video players.

15. A decoder, associated with and audio and video player, for use in a digital system that provides digital video and audio data, the decoder comprising:

a network interface for receiving the digital video and audio data;

a local clock;

video and audio decoders for decoding the received video and audio data;

video and audio drivers for driving the associated video and audio players; and

a controller that operates to adjust the local clock based on a master clock derived from content of the data, set a delay time in relation to the master clock, and adjust video and audio playback based on the delay, to substantially synchronize playback of the audio and video data by the audio and video players.

16. A decoder as claimed in claim 15, wherein:

the controller operates to adjust the local clock by initializing the local clock upon receipt of a program clock reference (PCR), and upon receipt of a subsequent PCR by the interface, adjusts the local clock based on a value of the local clock in relation to a presentation time stamp (PTS).

17. A decoder as claimed in claim 15, wherein:

the controller operates to adjust video and audio playback in relation to the master clock by establishing the delay time, and controlling the audio and video drivers to set playback times of the audio and video players such that upon receipt of the audio and video data, the audio and video players refrain from playing back the audio and video data for a time equal to the delay time.

18. A decoder as claimed in claim 15, wherein:

the controller operates to adjust video playback by comparing a time value at which a video frame is being presented by the video player in relation to a sum of a time of the master clock and the delay time, and controlling the video driver to operate the video player to restart, or to replay or skip the video frame, based on the comparison.

19. A decoder as claimed in claim 15, wherein:

the controller operates to adjust audio playback by comparing a time value at which a moment of audio is being presented by the audio player in relation to a sum of a time of the master clock and the delay time, and controlling the audio driver to operate the audio player to restart, skip ahead in the audio or refrain from presenting audio for a period, based on the comparison.

20. A decoder as claimed in claim 15, wherein

the controller operates to adjust a frequency of at least one of a playback clock associated with the video player and a playback clock associated with the audio player, in relation to a clock associated with a source that provides the digital and audio data.