Reduction of timing jitter in audio-video transport streams

Claim 1

A method of reducing program clock reference jitter in transport packets in a multiple program transport stream, the method comprising the steps of: processing program clock references for transport packets of one or more single program transport streams within the multiple program stream to generate corresponding dejittered program clock references as a function of clock frequency mismatch between a program clock and an asynchronous clock; generating a current cycle count for a current program clock reference indicative of the number of cycles of the asynchronous clock between the current program clock reference and a previous program clock reference; generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the mismatch estimate is a function of a sequence of jitter estimates for previous program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; generating a dejittered program clock reference for the current program clock reference as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate; and restamping the transport packets of the single program stream or streams with the corresponding dejittered program clock references.

Claim 2

A method of reducing program clock reference jitter in transport packets in a multiple program transport stream, the method comprising the steps of: processing program clock references for transport packets of one or more single program transport streams within the multiple program stream to generate corresponding dejittered program clock references as a function of clock frequency mismatch between a program clock and an asynchronous clock; generating a current cycle count for a current program clock reference indicative of the number of cycles of the asynchronous clock between the current program clock reference and a previous program clock reference; generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the mismatch estimate is a function of a sequence of jitter estimates for previous program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; generating a dejittered program clock reference for the current program clock reference as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate; and restamping the transport packets of the single program stream or streams with the corresponding dejittered program clock references.

Claim 7

A method of reducing program clock reference jitter in transport packets of a transport stream, the method comprising the steps of: determining the number of cycles of an asynchronous clock between receipt of program clock references for transport packets in the transport stream; generating dejittered program clock references as a function of the received program clock references and the number of asynchronous clock cycles; generating a current cycle count for a current program clock reference indicative of the number of cycles of the asynchronous clock between the current program clock reference and a previous program clock reference; generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the mismatch estimate is a function of a sequence of jitter estimates for previous program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; and generating a dejittered program clock reference for the current program clock reference as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate.

Claim 8

A method of reducing program clock reference jitter in transport packets of a transport stream, the method comprising the steps of: determining the number of cycles of an asynchronous clock between receipt of program clock references for transport packets in the transport stream; generating dejittered program clock references as a function of the received program clock references and the number of asynchronous clock cycles; generating a current cycle count for a current program clock reference indicative of the number of cycles of the asynchronous clock between the current program clock reference and a previous program clock reference; generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the mismatch estimate is a function of a sequence of jitter estimates for previous program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; and generating a dejittered program clock reference for the current program clock reference as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate.

Claim 13

An apparatus for reducing program clock reference jitter in transport packets of a transport stream, the apparatus comprising: a counter having an input connected to the output of an asynchronous clock and an output corresponding to a count of cycles of the asynchronous clock; a processor having a first input connected to the output of the counter and a second input connected to a source of program clock references of the transport stream, the processor having an output corresponding to dejittered program clock references generated in the processor as a function of the received program clock references and the asynchronous clock cycle count; wherein the processor further includes a phase-locked loop which generates an additive correction term to compensate for clock frequency mismatch between a program clock and the asynchronous clock; further wherein the phase-locked loop further includes: a first input for receiving from the counter a current cycle count for a current program clock reference; a filter for generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the current mismatch estimate is a function of a sequence of jitter estimates for program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; and an output corresponding to a dejittered program clock reference for the current program clock reference computed as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate.

Claim 14

An apparatus for reducing program clock reference jitter in transport packets of a transport stream, the apparatus comprising: a counter having an input connected to the output of an asynchronous clock and an output corresponding to a count of cycles of the asynchronous clock; a processor having a first input connected to the output of the counter and a second input connected to a source of program clock references of the transport stream, the processor having an output corresponding to dejittered program clock references generated in the processor as a function of the received program clock references and the asynchronous clock cycle count; wherein the processor further includes a phase-locked loop which generates an additive correction term to compensate for clock frequency mismatch between a program clock and the asynchronous clock; further wherein the phase-locked loop further includes: a first input for receiving from the counter a current cycle count for a current program clock reference; a filter for generating a current clock frequency mismatch estimate indicative of mismatch between a program clock and the asynchronous clock, wherein the current mismatch estimate is a function of a sequence of jitter estimates for program clock references, and further wherein a given jitter estimate is the difference between a program clock reference and its corresponding dejittered program clock reference; and an output corresponding to a dejittered program clock reference for the current program clock reference computed as a sum of (i) a previous dejittered program clock reference, (ii) the current cycle count, and (iii) a product of the current cycle count and the current clock frequency mismatch estimate.