Audio/video synchronization in a digital transmission system
AssigneeThomson Consumer Electronics, Inc.
InventorsDouglas E. Lankford, Michael S. Deiss
Life of this patent
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Abstract
A receiver (FIG. 2 ) for decoding associated compressed video and audio information components transmitted in mutually exclusive "frames" of data with respective time stamps PTS.sub.vid and PTS.sub.aud respectively, includes a controller (216) which is responsive to the respective received time stamps to provide coarse synchronization by delaying or skipping respective frames of one or the other of the components to approximately time align the two components. Fine synchronization is provided by adjusting the processing or clock frequency (215) of the audio signal processor (212) independent of the video processor (214). The control for the frequency adjustment is related to the difference between audio and video time stamps.
Claims14
Apparatus for providing synchronized, reproduced audio and video signals from recovered compressed audio and video signal, which audio and video signals include respective time stamps PTS.sub.aud and PTS.sub.vid determined at predetermined intervals and related to an encoder system clock, said apparatus comprising:
- a source (200) of said recovered compressed audio and video signals, and a source (208, 37) of reference frequency;
- a counter (208, 36) responsive to said reference frequency for providing a sequence of values modulo N where N is an integer;
- video signal decompression apparatus (214) responsive to said recovered compressed video signal for providing decompressed video signal and said time stamp PTS.sub.vid ;
- audio signal decompression apparatus (212) responsive to said recovered compressed audio signal for providing decompressed audio signal and said time stamp PTS.sub.aud ;
- means (222, 217) for capturing values (LVS) of said sequence at predetermined times related to reception of video time stamps PTS.sub.vid and for generating differences (.DELTA..sub.V-PTS) between said values LVS and corresponding time stamps PTS.sub.vid ;
- and (220, 218) for capturing values (LAS) of said sequence at predetermined times related to reception of audio time stamps PTS.sub.aud and generating differences (.DELTA..sub.A-PTS) between said values LAS and corresponding time stamps PTS.sub.aud ;
- and
- means (219, 216, 215) responsive to said differences (.DELTA..sub.V-PTS) and (.DELTA..sub.A-PTS) for synchronizing the decompressed audio and video signals.
Apparatus for providing synchronized, reproduced audio and video signals from recovered compressed audio and video signal, which audio and video signals include respective time stamps PTS.sub.aud and PTS.sub.vid determined at predetermined intervals and related to an encoder system clock, said apparatus comprising:
- a source (200) of said recovered compressed audio and video signals, and a source (208) of a local clock signal;
- video signal decompression apparatus (214) responsive to said recovered compressed video signal for providing decompressed video signal and said time stamp PTS.sub.vid ;
- audio signal decompression apparatus (212) responsive to said recovered compressed audio signal for providing decompressed audio signal and said time stamp PTS.sub.aud ;
- means (217, 218, 219, 220, 222) for determining, in cycles of said local clock signal, times T between reception of corresponding time stamps PTS.sub.aud and PTS.sub.vid ;
- means (219) for calculating the difference between values of corresponding time stamps PTS.sub.aud and PTS.sub.vid and comparing such difference with said time T to generate an A/V synchronization error signal;
- and
- means (215, 216) responsive to said A/V synchronization error signal for synchronizing the decompressed audio and video signals.
Apparatus for providing synchronized, reproduced audio and video signals from recovered compressed audio and video signal, which recovered audio and video signals include respective time stamps PTS.sub.aud and PTS.sub.vid determined at predetermined intervals in an encoder and related to a system clock at said encoder, said apparatus comprising audio decompression apparatus for decompressing said compressed audio signal and video decompression apparatus for decompressing compressed video signal and respectively producing from compressed audio and video signals said time stamps PTS.sub.aud and PTS.sub.vid ;
- and means responsive to the reception of said time stamps PTS.sub.aud and PTS.sub.vid for measuring times between reception of a PTS.sub.aud and a next occurring PTS.sub.vid and adjusting a rate of decompression of at least one of said audio and video decompression apparatus such that the time between a reception of a PTS.sub.aud and the reception of a next occurring PTS.sub.vid substantially equals the difference in values of said PTS.sub.aud and the next occurring PTS.sub.vid.
Dependencies are inferred from the claim text.