Timing correction method and apparatus

• US 6,101,195 A
• Filed: 05/28/1997
• Issued: 08/08/2000
• Est. Priority Date: 05/28/1997
• Status: Expired due to Term

• Current Assignee: Invidi Technologies Corporation
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Lyons, Paul Wallace, Acampora, Alfonse Anthony, Beltz, John Prickett
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Bayard, Emmanuel
• Application Number:
  US08/864,326
• Time in Patent Office: 1,168 Days
• Field of Search: 375/316, 375/354, 375/355, 375/377, 375/372, 370/389, 370/407, 370/468, 370/498, 348/512, 348/513
• US Class Current: 370/498
• CPC Class Codes: H04N 21/23424 involving splicing one content stream with another content stream, e.g. for inserting or substituting an advertisement
• CPC Class Codes: H04N 21/23605 Creation or processing of packetized elementary streams [PES]
• CPC Class Codes: H04N 21/23608 Remultiplexing multiplex streams, e.g. involving modifying time stamps or remapping the packet identifiers
• CPC Class Codes: H04N 21/242 Synchronization processes, e.g. processing of PCR [Program Clock References] arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• 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 21/4344 Remultiplexing of multiplex streams, e.g. by modifying time stamps or remapping the packet identifiers
• CPC Class Codes: H04N 21/44004 involving video buffer management, e.g. video decoder buffer or video display buffer
• CPC Class Codes: H04N 21/44016 involving splicing one content stream with another content stream, e.g. for substituting a video clip
• CPC Class Codes: H04N 5/04 Synchronising for television systems using pulse code modulation H04N7/56
• 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

Abstract

An apparatus and method for receiving an information stream comprising a plurality of timing portions and associated payload portions, decoding each timing portion, determining a duration parameter of a payload portion associated with the decoded timing portion, and recoding the timing portion using the duration parameter and a local reference time parameter.

Claims

1. A time base correction method comprising the steps of:

(A) receiving an information stream, said received information stream comprising a compressed video stream having a plurality of timing portions and associated payload portions, said timing portions being necessary for decoding said associated payload portions to produce a video program at a decoder;

(B) decoding a timing portion including a presentation time stamp of said information stream;

(C) determining a duration parameter of a payload portion associated with said decoded timing portion;

(D) modifying said decoded presentation time stamp using said duration parameter to form a new presentation time stamp;

(E) recoding said timing portion including said new presentation time stamp of said information stream; and

(F) repeating steps (B) through (D) for each of said plurality of timing portions and associated payload portions of said received information stream to produce an output information stream, said output information stream comprising said compressed video stream, said compressed video stream including modified timing portions.

2. The method of claim 1 wherein:

step (C) further comprises the step of determining a size parameter of said payload portion associated with said decoded timing portion; and

step (D) further comprises the steps of;

comparing said duration parameter to a decode buffer utilization parameter; and

responsively reducing a rate of receiving said information stream if said comparison indicates that said decode buffer utilization exceeds a predetermined threshold level.

3. The method of claim 2 wherein:

step (D) further comprises the step of;

responsively increasing a rate of receiving said information stream if said comparison indicates that said decode buffer utilization is less than a predetermined threshold level.

4. The method of claim 1 wherein:

step (C) further comprises the step of determining a size parameter of said payload portion associated with said decoded timing portion; and

step (D) further comprises the steps of;

comparing said duration parameter to a decode buffer utilization parameter; and

responsively reducing a rate of receiving said information stream if said comparison indicates that said decode buffer utilization exceeds a predetermined threshold level.

5. A method for retiming a bitstream, said bitstream comprising timing portions and respective compressed payload portions, said method comprising the steps of:

generating a local time stamp in response to a local timing signal;

retrieving a presentation time stamp from said timing portions of said bitstream;

adding time stamp to produce a new presentation time stamp; and

inserting said new presentation time stamp into said bitstream to produce a retimed bitstream, said retimed bitstream comprising retimed portions and respective compressed payload portions.

6. The method of claim 5 further comprising the steps of:

retrieving a decode time stamp from said timing portions of said bitstream;

subtracting said retrieved decode time stamp from said new presentation time stamp; and

inserting said generated time stamp into said bitstream as new decode time stamp.

7. The method of claim 5, wherein said generating step comprises the steps of:

adding a delay parameter to said local timing source signal to produce an adjusted timing signal; and

storing said adjusted timing signal in response to a control signal representative of the start of an information packet in said bitstream.

8. The method of claim 7, further comprising the steps of:

producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream;

comparing said adjusted timing signal to said stored timing signal; and

in the case of said adjusted timing signal exceeding said stored timing signal, causing said buffer control signal to indicate that said desired flow is reduced;

in the case of said stored timing signal exceeding said adjusted timing signal, causing said buffer control signal to indicate that said desired flow is increased.

9. The method of claim 7, further comprising the steps of:

producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream;

subtracting said generated time stamp from said adjusted timing signal to produce a first difference signal;

comparing said first difference signal to a buffer delay parameter associated with said bitstream; and

in the case of said first difference signal exceeding said buffer delay parameter associated with said bitstream, causing said buffer control signal to indicate that said desired flow is increased;

in the case of said buffer delay parameter associated with said bitstream exceeding said first difference signal, causing said buffer control signal to indicate that said desired flow is decreased.

10. The method of claim 7, further comprising the steps of:

producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream;

monitoring an indicium of the number of bytes in a decoder buffer; and

in the case of said number of bytes in said decoder buffer exceeding a predetermined maximum amount, causing said buffer control signal to indicate that said desired flow is decreased;

in the case of said number of bytes in said decoder buffer being below a predetermined minimum amount, causing said buffer control signal to indicate that said desired flow is increased.

11. Apparatus suitable for retiming a bitstream in response to a local timing source, said bitstream comprising timing portions and respective encoded payload portions said timing portion being useful in decoding respective payload portions, said apparatus comprising:

a time stamp generator, responsive to a timing signal, for generating a time stamp;

a first decoder for retrieving a presentation time stamp from said timing portions of said bitstream;

an adder for adding said generated time stamp to said retrieved presentation time stamp to produce a new presentation time stamp; and

a multiplexer, coupled to said adder, for inserting said new presentation time stamp into said bitstream to produce a retimed bitstream, said retimed bitstream comprising retimed timing portions and respective encoded payload portions.

12. The apparatus of claim 11 further comprising:

a second decoder for retrieving a decode time stamp from said timing portions of said bitstream; and

a subtractor for subtracting said retrieved decode time stamp from said new presentation time stamp;

said multiplexer inserting said generated time stamp into said bitstream as a new decode time stamp.

13. The apparatus of claim 11, wherein:

said time stamp generator comprises;

an adder, for adding a delay parameter to said timing signal, to produce an adjusted timing signal; and

a storage element for storing said adjusted timing signal in response to a control signal representative of the start of an information packet in said bitstream.

14. The apparatus of claim 13 further comprising:

a logic unit for producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream; and

a first comparator, coupled to said time stamp generator and said logic unit, for comparing said adjusted timing signal to said stored adjusted timing signal and responsively producing an output signal;

said logic unit, in response to said first comparator output signal indicating that said adjusted timing signal exceeds said stored adjusted timing signal, causing said buffer control signal to indicate that said desired flow is reduced; and

said logic unit, in response to said first comparator output signal indicating that said stored adjusted timing signal exceeds said adjusted timing signal, causing said buffer control signal to indicate that said desired flow is increased.

15. The apparatus of claim 13 further comprising:

a logic unit for producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream;

a second subtractor, coupled to said timing generator and said timing source, for subtracting said generated time stamp from said adjusted timing signal to produce a first difference signal; and

a second comparator, coupled to said second subtractor and said logic unit, for comparing said first difference signal to a buffer delay parameter associated with said bitstream;

said logic unit, in response to said second comparator output signal indicating that said first difference signal exceeds said buffer delay parameter associated with said bitstream, causing said buffer control signal to indicate that said desired flow is increased;

said logic unit, in response to said second comparator output signal indicating that said buffer delay parameter associated with said bitstream exceeds said first difference signal, causing said buffer control signal to indicate that said desired flow is decreased.

16. The apparatus of claim 13 further comprising:

a logic unit for producing a buffer control signal, said buffer control signal indicative of a desired flow of data in said bitstream; and

a frame byte counter, coupled to said logic unit, for counting a number of bytes stored in a decoder buffer;

said logic unit, in response to said number of bytes stored in said decoder buffer exceeding a predetermined maximum amount, causing said buffer control signal to indicate that said desired flow is decreased;

said logic unit, in response to said number of bytes stored in said decoder buffer being below a predetermined minimum amount, causing said buffer control signal to indicate that said desired flow is increased.

17. The apparatus of claim 11 wherein said output bitstream comprises a packetized elementary stream and said apparatus further comprises:

a transport stream encoder, coupled to said multiplexer output, for transport encoding said output bitstream to produce a transport encoded bitstream.

18. The apparatus of claim 17 wherein said transport stream encoder receives a second bitstream from a second bitstream source, and said transport encoded bitstream comprises at least said output bitstream from said multiplexer and said second bitstream.

19. The apparatus of claim 14 further comprising:

a frame byte counter, coupled to said logic unit, for counting a number of bytes stored in a decoder buffer;

said logic unit, in response to said number of bytes stored in said decoder buffer exceeding a predetermined maximum amount, causing said buffer control signal to indicate that said desired flow is decreased; and

said logic unit, in response to said number of bytes stored in said decoder buffer being below a predetermined minimum amount, causing said buffer control signal to indicate that said desired flow is increased.

20. The apparatus of claim 15 further comprising:

a frame byte counter, coupled to said logic unit, for counting a number of bytes stored in a decoder buffer;

said logic unit, in response to said number of bytes stored in said decoder buffer exceeding a predetermined maximum amount, causing said buffer control signal to indicate that said desired flow is decreased; and

said logic unit, in response to said number of bytes stored in said decoder buffer being below a predetermined minimum amount, causing said buffer control signal to indicate that said desired flow is increased.

21. The apparatus of claim 13 wherein said output bitstream comprises a packetized elementary stream and said apparatus further comprises:

a transport stream encoder, coupled to said multiplexer output, for transport encoding said output bitstream to produce a transport encoded bitstream.