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Synchronized, variable-speed playback of digitally recorded audio and video

  • US 5,664,044 A
  • Filed: 03/27/1996
  • Issued: 09/02/1997
  • Est. Priority Date: 04/28/1994
  • Status: Expired due to Term
First Claim
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1. A method of maintaining synchronization of a stream of digital audio data with a stream of digital video data originally recorded at a specified rate in frames per second, FPS, the digital video data being played back on a variable-speed audio/video display system using a user-selected scaling factor, RV, which is set to a proportional value of a recorded rate, the method comprising the steps of:

  • placing at least 2 frames of digital audio in an audio buffer and at least 2 frames of digital video in a video buffer;

    setting an audio time domain harmonic scaling factor, C, equal to the user-selected scaling factor, RV;

    calculating an amount of time in seconds, T, required to play back an audio frame with the selected audio time domain harmonic scaling factor C;

    decoding and displaying, if the video buffer is not empty, a frame of video from the video buffer for T seconds;

    decoding, scaling and playing, if the audio buffer is not empty, an audio frame from the audio buffer using the audio time domain harmonic scaling factor C so that playback of the audio frame requires an audio playback time period equal to T seconds;

    reading, after T seconds, and if the end of the stream of digital audio data or the stream of digital video data has not been reached, another frame from the stream of digital audio into the audio buffer and another frame from the stream of digital video into the video buffer;

    determining whether the audio playback time period of the audio frame played during the preceding time period T was exactly equal to T seconds;

    adjusting the value C if the audio playback time period was not exactly equal to T seconds; and

    recalculating the time T if the audio time domain harmonic scaling factor C has changed since the beginning of the preceding time period T.

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