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System and method for synchronizing operations among a plurality of independently clocked digital data processing devices

  • US 8,234,395 B2
  • Filed: 04/01/2004
  • Issued: 07/31/2012
  • Est. Priority Date: 07/28/2003
  • Status: Active Grant
First Claim
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1. A method for synchronizing audio playback of a plurality of separate audio playing devices with one another, the method comprising:

  • receiving, by a playback device, a multicast stream including a plurality of frames from a source device over a local network, wherein each frame of the plurality of frames is associated with audio information and a time indicating when to play the audio information of the respective frame, wherein the time is based on a clock of the source device, which is independent of a clock of the playback device;

    periodically receiving, by the playback device, a unicast message transmitted from the source device, the unicast message separate from the multicast stream and including clock information of the source device;

    computing, by the playback device, a time differential between the clock of the source device and the clock of the playback device based on a most recently received unicast message;

    converting, by the playback device and for each frame of the plurality of frames, a computed output time of the audio information for each respective frame, the converting based on both the time associated with each respective frame and a most recent computation of the time differential;

    outputting, by the playback device, audio information based on the plurality of frames by playing audio information for each respective frame based on a clock of the playback device, wherein the playback device is configured to output the audio information in synchrony with the source device; and

    adjusting a speed at which the playback device outputs the audio information, wherein the speed is adjusted based on a comparison between an expected output time of audio information for a particular frame and the computed output time of the particular frame.

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