Error detection and recovery for high rate isochronous data in MPEG-2 data streams

• US 5,742,623 A
• Filed: 07/11/1996
• Issued: 04/21/1998
• Est. Priority Date: 08/04/1995
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Moroney, Paul, Nuber, Ray
• Primary Examiner(s): Baker, Stephen M.
• Application Number:
  US08/678,108
• Time in Patent Office: 649 Days
• Field of Search: 371/47.1, 371/57.1, 371/57.2, 371/61, 371/65
• US Class Current: 714/798
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04N 19/895 in combination with error concealment
• CPC Class Codes: H04N 21/43072 of multiple content streams on the same device
• CPC Class Codes: H04N 21/4343 Extraction or processing of packetized elementary streams [PES]
• CPC Class Codes: H04N 21/4348 Demultiplexing of additional data and video streams
• 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 7/54 the signals being synchronous H04N21/23602, H04N21/23614, H04N21/2365, H04N21/2368, H04N21/4341, H04N21/4342, H04N21/4347, H04N21/4348 take precedence
• CPC Class Codes: H04N 7/56 Synchronising systems therefor

Abstract

Error recovery is provided for isochronous data ("isodata") obtained from a data stream. Isodata transport packets are monitored to locate isodata presentation time stamps (PTSs). The presentation of isodata from a buffer is synchronized to a system time clock (STC) using timing information derived from the PTSs. Discontinuity errors between said isodata transport packets are identified and, if a discontinuity of no more than one packet is identified, a write pointer of the buffer is advanced by a suitable number of bits to compensate for the discontinuity, while maintaining the synchronization of the presentation with respect to the STC. Additional error detection and recovery techniques are disclosed, including the maintenance of a presentation unit counter, the use of a PTE extension and PTS offset to verify output timing, the provision of a pair of PTS pointers verifying correct output data timing, the use of a packet elementary stream (PES) count to detect lost data in the transport stream, and the detection and discarding of packets designated as encrypted after any decryption should have already been completed.

Claims

1. A method for managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PID) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said method comprising the steps of:

monitoring said data stream to detect PIDs identifying said isodata transport packets;

monitoring the isodata transport packets identified by said PIDs to locate isodata PTSs;

synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) using timing information derived from the located isodata PTSs;

identifying discontinuity errors between successive ones of said isodata transport 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.

2. A method in accordance with claim 1 wherein first and second PTS pointers are provided, each for maintaining a different PTS value and address of said buffer identifying where a presentation unit referred to by the PTS value is stored, the synchronization of said presentation being maintained by the further steps of:

replacing the PTS value and address for one of said PTS pointers with a new PTS value and new address after data stored at the address associated with the replaced value has been presented from said buffer;

when said new address is reached, suspending the presentation of data from said buffer if said STC is not equal to a presentation time derived from said new PTS value; and

if said presentation has been suspended, recommencing the presentation of data from said buffer when said STC reaches said presentation time derived from said new PTS value.

3. A method in accordance with claim 2 wherein new PTS values are received over time from said isodata transport packets, said method comprising the further steps of:

determining if both of said PTS pointers contain PTS values that have not yet been used to present data from said buffer when a new PTS value is received; and

if so,

replacing the PTS value and associated address in the most recently updated PTS pointer with the new PTS value and new address, thereby maintaining the oldest unused PTS value and address for use in synchronizing the presentation of said presentation units from said buffer.

4. A method in accordance with claim 1 wherein a PTS pointer is provided to maintain a current PTS value together with an address of said buffer identifying where a presentation unit referred to by said current PTS value is stored, the synchronization of said presentation being maintained by the further steps of:

replacing said PTS value in said PTS pointer with a new current PTS value after data stored at said address has been presented from said buffer;

replacing said address in said PTS pointer with a new address corresponding to a presentation unit referred to by said new current PTS value;

when said new address is reached, suspending the presentation of data from said buffer if said STC is not equal to a presentation time derived from said new current PTS value; and

if said presentation has been suspended, recommencing the presentation of data from said buffer when said STC reaches said presentation time derived from said new current PTS value.

5. A method in accordance with claim 4 wherein the presentation units carried by said packetized data stream are supplied by packetized elementary stream (PES) packets carrying the presentation units together with information indicative of the length of each PES packet, said method comprising the further steps of:

determining if an amount of presentation unit data actually received for a given PES packet differs from an amount of data that should be received as indicated by the PES packet length information; and

indicating an error if the compared amounts of data do not match.

6. A method in accordance with claim 5 comprising the further steps of:

clearing said PTS pointer and temporarily stalling the presentation of data from said buffer in the event additional presentation unit data continues to arrive in the absence of a new PES packet indicator after said PES packet length information indicates that all data has been provided for said given PES packet; and

recommencing the presentation of data from said buffer based on a new PTS value provided in said PTS pointer after the PTS pointer has been cleared.

7. A method in accordance with claim 5 wherein first and second PTS pointers are provided, each for maintaining a different PTS value and address of said buffer identifying where a presentation unit referred to by the PTS value is stored, with new PTS values being received over time from said isodata transport packets, said method comprising the further steps of:

determining if both of said PTS pointers contain PTS values that have not yet been used to present data from said buffer when a new PTS value is received, and if so,

replacing the PTS value and associated address in the most recently updated PTS pointer with the new PTS value and new address, thereby maintaining the oldest unused PTS value and address for use in synchronizing the presentation of said presentation units from said buffer;

clearing both of said PTS pointers and temporarily stalling the presentation of data from said buffer in the event additional presentation unit data continues to arrive in the absence of a new PES packet indicator after said PES packet length information indicates that all data has been provided for said given PES packet; and

recommencing the presentation of data from said buffer based on a new PTS value provided in one of said PTS pointers after the PTS pointers have been cleared.

8. A method in accordance with claim 1 wherein;

the isodata presentation units carried in said fixed length isodata transport packets are obtained from isodata packetized elementary stream (PES) packets, and

said suitable number of bits for advancing said write pointer is determined in response to a count of PES payload bytes retrieved from the isodata transport packets.

9. A method in accordance with claim 8 wherein said fixed length isodata transport packets each comprise 188 bytes, and;

if said count indicates that at least 184 bytes remain to be received for said current PES packet, said count is decremented by 184 and said write pointer is advanced by 184 byte addresses;

if said count indicates that no bytes remain to be received for the current PES packet, said count is set to the value of a previous PES packet length and then decremented by 178, and said write pointer is advanced by 164 byte addresses; and

if said count indicates that N bytes, where 1≦

N≦

183 remain to be received for said current PES packet, said count is decremented by N and said write pointer is advanced by N byte addresses.

10. A method for managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PIP) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said method comprising the steps

monitoring said data stream to detect PIDs identifying said isodata transport packets;

monitoring the isodata transport packets identified by said PIPs to locate isodata PTSs;

synchronizing the presentation of said presentation units from said buffer no a system time clock (STC) using timing information derived from the located isodata PTSs, said synchronization step comparing the STC to the timing information derived from the PTSs; and

providing fill bits as output until it is time to present said presentation units if said comparison determines that said presentation units are too early to be presented.

11. A method in accordance with claim 10 comprising the further steps of:

retrieving a PTS extension from the identified isodata transport packets to enable the time resolution for presenting isodata presentation units to be increased; and

deriving said timing information by summing at least said PTS and said PTS extension.

12. A method in accordance with claim 11 wherein said timing information is derived from the sum of said PTS, said PTS extension, and a PTS offset value used to provide a time delay.

13. A method in accordance with claim 11 comprising the further steps of:

comparing said timing information to said STC to determine whether said presentation units are too late to be presented or ready to be presented from said buffer;

resynchronizing the presentation of presentation units from said buffer if said comparing step determines that said presentation units would otherwise be presented too late; and

presenting said presentation units from said buffer if said comparing step determines that said presentation units are ready to be presented.

14. A method in accordance with claim 10 wherein:

said timing information comprises the sum of at least a PTS and a PTS extension that enables the time resolution for presenting isodata presentation units to be increased; and

said fill bits are provided as output until a time designated by the STC equals the time designated by said sum.

15. A method in accordance with claim 14 wherein said timing information comprises the sum of said PTS, said PTS extension, and a PTS offset value used to provide a time delay.

16. A method in accordance with claim 14 wherein each presentation unit comprises an integer number N bits of isodata, said method comprising the further steps of:

maintaining an N-bit count that is correlated with the presentation of a first presentation unit from said buffer; and

continuing to provide fill bits as output after said STC equals the time designated by said sum until said N-bit count indicates that it is time to commence the presentation of a new presentation unit.

17. A method for managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PID) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said method comprising the steps of:

monitoring said data stream to detect PIDs identifying said isodata transport packets;

monitoring the isodata transport packets identified by said PIDs to locate isodata PTSs;

synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) using timing information derived from the located isodata PTSs, said synchronization step comparing the STC to the timing information derived from the PTSs;

monitoring said isodata transport packets identified by said PIDs to determine if any of them are designated as being encrypted after any encryption should have been removed; and

if a single packet only is designated as being encrypted after any encryption should have been removed, advancing a write pointer of said buffer by a suitable number of bits to ignore the single packet, while maintaining the synchronization of said presentation with respect to said STC.

18. A decoder for receiving and managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PID) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said decoder comprising:

means for monitoring said data stream to detect PIDs identifying said isodata transport packets;

means for monitoring the isodata transport packets identified by said PIDs to locate isodata PTSs;

means for synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) using timing information derived from the located isodata PTSs;

means for identifying discontinuity errors between successive ones of said isodata transport 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.

19. A decoder in accordance with claim 18 wherein first and second PTS pointers are provided, each for maintaining a different PTS value and address of said buffer identifying where a presentation unit referred to by the PTS value is stored, the synchronization of said presentation being maintained by means for:

replacing the PTS value and address for one of said PTS pointers with a new PTS value and new address after data stored at the address associated with the replaced value has been presented from said buffer;

when said new address is reached, suspending the presentation of data from said buffer if said STC is not equal to a presentation time derived from said new PTS value; and

recommencing the presentation of data from said buffer when said STC reaches said presentation time derived from said new PTS value if said presentation has been suspended.

20. A decoder in accordance claim 19 wherein new PTS values are received over time from said isodata transport packets, said decoder further comprising:

means for determining if both of said PTS pointers contain PTS values that have not yet been used to present data from said buffer when a new PTS value is received; and

means responsive to said determining means when neither of the PTS values in said pointers have been used when a new PTS value is received, for replacing the PTS value and associated address in the most recently updated PTS pointer with the new PTS value and new address, thereby maintaining the oldest unused PTS value and address for use in synchronizing the presentation of said presentation units from said buffer.

21. A decoder in accordance with claim 18 wherein a PTS pointer is provided to maintain a current PTS value together with an address of said buffer identifying where a presentation unit referred to by said current PTS value is stored, the synchronization of said presentation being maintained by means for:

replacing said PTS value in said PTS pointer with a new current PTS value after data stored at said address has been presented from said buffer;

replacing said address in said PTS pointer with a new address corresponding to a presentation unit referred to by said new current PTS value;

suspending the presentation of data from said buffer if said STC is not equal to a presentation time derived from said new current PTS value when said new address is reached; and

recommencing the presentation of data from said buffer when said STC reaches said presentation time derived from said new current PTS value if said presentation has been suspended.

22. A decoder in accordance with claim 21 wherein the presentation units carried by said packetized data stream are supplied by packetized elementary stream (PES) packets carrying the presentation units together with information indicative of the length of each PES packet, said decoder further comprising:

means for determining if an amount of presentation unit data actually received for a given PES packet differs from an amount of data that should be received as indicated by the PES packet length information; and

means responsive to said determining means for indicating an error if the compared amounts of data do not match.

23. A decoder in accordance with claim 22 further comprising:

means for clearing said PTS pointer and temporarily stalling the presentation of data from said buffer in the event additional presentation unit data continues to arrive in the absence of a new PES packet indicator after said PES packet length information indicates that all data has been provided for said given PES packet; and

means for recommencing the presentation of data from said buffer based on a new PTS value provided in said PTS pointer after the PTS pointer has been cleared.

24. A decoder in accordance with claim 22 wherein first and second PTS pointers are provided, each for maintaining a different PTS value and address of said buffer identifying where a presentation unit referred to by the PTS value is stored, with new PTS values being received over time from said isodata transport packets, said decoder further comprising means for:

determining if both of said PTS pointers contain PTS values that have not yet been used to present data from said buffer when a new PTS value is received, and if so,

replacing the PTS value and associated address in the most recently updated PTS pointer with the new PTS value and new address, thereby maintaining the oldest unused PTS value and address for use in synchronizing the presentation of said presentation units from said buffer;

clearing both of said PTS pointers and temporarily stalling the presentation of data from said buffer in the event additional presentation unit data continues to arrive in the absence of a new PES packet indicator after said PES packet length information indicates that all data has been provided for said given PES packet; and

recommencing the presentation of data from said buffer based on a new PTS value provided in one of said PTS pointers after the PTS pointers have been cleared.

25. A decoder in accordance with claim 18 wherein:

the isodata presentation units carried in said fixed length isodata transport packets are obtained from isodata packetized elementary stream (PES) packets, and

a counter provides a count of PES payload bytes retrieved from the isodata transport packets, said suitable number of bits for advancing said write pointer being determined in response to said count.

26. A decoder in accordance with claim 25 wherein said fixed length isodata transport packets each comprise 188 bytes, and:

if said count indicates that at least 184 bytes remain to be received for said current PES packet, said count is decremented by 184 and said write pointer is advanced by 184 byte addresses;

if said count indicates that no bytes remain to be received for the current PES packet, said count is set to the value of a previous PES packet length and then decremented by 178, and said write pointer is advanced by 164 byte addresses; and

if said count indicates that N bytes, where 1≦

N≦

183 remain to be received for said current PES packet, said count is decremented by N and said write pointer is advanced by N byte addresses.

27. A decoder for receiving and managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PID) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said decoder comprising:

means for monitoring said data stream to detect PIDs identifying said isodata transport packets;

means for monitoring the isodata transport packets identified by said PIDs to locate isodata PTSs;

means for synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) using timing information derived from the located isodata PTSs; and

means for providing fill bits as output until it is time to present said presentation units if said comparison determines that said presentation units are too early to be presented.

28. A decoder in accordance with claim 27 further comprising:

means for retrieving a PTS extension from the identified isodata transport packets to enable the time resolution for presenting isodata presentation units to be increased; and

an adder for summing at least said PTS and said PTS extension to provide said timing information.

29. A decoder in accordance with claim 28 wherein said adder provides said timing information by summing said PTS, said PTS extension, and a PTS offset value used to provide a time delay.

30. A decoder in accordance with claim 28 further comprising:

means for comparing said timing information to said STC to determine whether said presentation units are too late to be presented or ready to be presented from said buffer;

means for resynchronizing the presentation of presentation units from said buffer if said comparing step determines that said presentation units are too late to be presented; and

means for presenting said presentation units from said buffer if said comparing step determines that said presentation units are ready to be presented.

31. A decoder in accordance with claim 27 further comprising an adder for providing said timing information by summing at least a PTS and a PTS extension that enables the time resolution for presenting isodata presentation units to be increased, wherein:

said fill bits are provided as output until a time designated by the STC equals a time designated by said timing information.

32. A decoder in accordance with claim 31 wherein said adder computes said timing information by summing said PTS, said PTS extension, and a PTS offset value used to provide a time delay.

33. A decoder in accordance with claim 31 wherein each presentation unit comprises an integer number N bits of isodata, said decoder further comprising:

an N-bit counter that is correlated with the presentation of a first presentation unit from said buffer;

wherein said fill bits continue to be provided as output after said STC equals the time designated by said sum until said N-bit counter indicates that it is time to commence the presentation of a new presentation unit.

34. A decoder for receiving and managing errors in isochronous data ("isodata") received in bursts from a packetized data stream carrying isodata presentation units in fixed length isodata transport packets, each of said transport packets including a packet identifier (PID) and at least some of said packets containing a presentation time stamp (PTS) indicative of a time for commencing the fixed rate presentation of isodata presentation units from a buffer into which they are temporarily stored upon receipt, said decoder comprising:

means for monitoring said data stream to detect PIDs identifying said isodata transport packets;

means for monitoring the isodata transport packets identified by said PIDs to locate isodata PTSs;

means for synchronizing the presentation of said presentation units from said buffer to a system time clock (STC) using timing information derived from the located isodata PTSs, said synchronization step comparing the STC to the timing information derived from the PTSs;

means for determining if any of the isodata transport packets identified by said PIDs are identified as being encrypted after any encryption should have been removed; and

means responsive to said determining means when a single packet only is designated as being encrypted after any encryption should have been removed, for advancing a write pointer of said buffer by a suitable number of bits to ignore the single packet while maintaining the synchronization of said presentation with respect to said STC.