Acquisition and error recovery of audio data carried in a packetized data stream

A method for processing digital audio data from a packetized data stream carrying digital television information in a succession of transport packets having a fixed length of N bytes, each of said packets including a packet identifier (PID), some of said packets containing a program clock reference (PCR) value for synchronizing a decoder system time clock, and some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the output of associated data for use in reconstructing a television signal, said method comprising the steps of:

• monitoring the PID's for the packets carried in said data stream to detect audio packets;
• examining the detected audio packets to locate the occurrence of audio synchronization words for use in achieving a synchronization condition, each two consecutive audio synchronization words defining an audio frame therebetween;
• monitoring the detected audio packets after said synchronization condition has been achieved to locate an audio PTS;
• searching the detected audio packets after locating said audio PTS to locate the next audio synchronization word;
• storing audio data following said next audio synchronization word in a buffer;
• detecting the occurrence of errors in said audio packets;
• upon detecting a first audio packet of a current audio frame containing an error, advancing a write pointer for said buffer by N bytes and designating said current audio frame as being in error;
• monitoring the detected audio packets of said current audio frame for the next audio synchronization word after said error has been detected, and if said synchronization word is not received where expected in the audio stream, discarding subsequent audio data while searching for said synchronization word rather than storing the subsequent audio data into said buffer;
• resuming the storage of audio data in said buffer upon detection of said next audio synchronization word if said next audio synchronization word is located within N bytes after the commencement of the search therefor;
• and
• if said next audio synchronization word is not located within said N bytes after the commencement of the search therefor, commencing a reacquisition of said synchronization condition.

Apparatus for acquiring audio information carried by a packetized data stream and processing errors therein, comprising:

• means for detecting audio transport packets in said data stream;
• means for recovering audio data from said detected audio transport packets for storage in a buffer;
• means for locating an audio presentation time stamp (PTS) in said detected audio transport packets;
• means responsive to said PTS for commencing the output of audio data from said buffer at a specified time;
• means for monitoring the detected audio transport packets after the output of audio data from said buffer has commenced, to locate subsequent audio PTS's;
• means for comparing a time derived from a decoder system time clock (STC) to a time derived from the subsequent audio PTS's to determine whether audio data stored in said buffer is too early to decode, too late to decode, or ready to be decoded;
• and
• means responsive to said comparing means for adjusting the time at which said stored audio data is output from said buffer.

Apparatus for acquiring audio information carried by a packetized data stream and processing errors therein, comprising:

• means for detecting audio transport packets in said data stream, said packets being arranged into successive audio frames commencing with an audio synchronization word;
• means responsive to said synchronization words for obtaining a synchronization condition enabling the recovery of audio data from said detected audio transport packets for storage in a buffer;
• means for detecting the presence of errors in said audio data;
• means responsive to said error detecting means for controlling the flow of data through said buffer when an error is present, to attempt to maintain said synchronization condition while masking said error;
• and
• means for reestablishing the detection of said audio transport packets if said controlling means cannot maintain said synchronization condition.

A method for managing errors in data received in bursts from a packetized data stream carrying digital information in a succession of fixed length transport packets, at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of presentation units from a buffer into which they are temporarily stored upon receipt, said method comprising the steps of:

• monitoring received packets to locate associated PTS's, said received packets carrying presentation units to be presented;
• synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) associated with the packetized data stream using timing information derived from the PTS's located in said monitoring step;
• and
• identifying discontinuity errors resulting from a loss of one or more transmitted packets between successive ones of the received packets and, if a discontinuity of no more than one packet is identified, advancing a write pointer of said buffer by a suitable number of bits to compensate for the discontinuity, while maintaining the synchronization of said presentation with respect to said STC.