MPEG information signal conversion system

A method of processing a first transport stream of transport packets having a PCR comprising plural bits representing valid timing-critical-information, and of unknown transport rate that may be of varying rate or bursty, to form a second transport stream of transport packets of known constant rate and of valid timing-critical-information, comprising the steps:

• (i) providing a local clock,
• (ii) processing the transport packets of the first transport stream in a serial manner while sampling the local clock when one bit of the PCR of each packet is processed and storing the sampled clock time for each packet,
• (iii) delaying the transport packets to avoid overflowing a downstream buffer,
• (iv) when ready to deliver the transport packets without overflowing the downstream buffer, re-processing the transport packets while re-sampling the local clock and determining for each transport packet a new sample time corresponding to the time of reprocessing of said one PCR bit and updating the PCR with the new sample time,
• (v) delivering the transport packets with updated PCRs to form the second transport stream.

A method of transmitting timing-critical data including a program clock reference (PCR) via an asynchronous channel downstream to apparatus including a target buffer having a limited read-out rate, comprising the steps:

• (i) receiving the timing-critical data subdivided into a stream of successive transport packets,
• (ii) determining the arrival time of each of the transport packets,
• (iii) temporarily storing the transport packets,
• (iv) computing the times when individual transport packets can be transmitted downstream to avoid overflowing the target buffer,
• (v) computing the departure time of each of said transport packets and modifying the PCR accordingly,
• (vi) transmitting downstream the transport packets in accordance with the computations of step (iv).

Apparatus for generating from an incoming unknown first transport stream of transport packets having a PCR and of valid timing-critical-information a fixed-rate constant second transport stream comprising a sequence of transport packets comprising a PCR for delivery to a target buffer having a maximum read-out rate, comprising:

• (a) filter means for receiving the first transport stream for passing the transport packets desired to be included in the second transport stream,
• (b) a local clock measuring time,
• (c) a transport packet store for receiving the packets of the first transport stream,
• (d) a scheduler for storing the maximum read-out rate of the target buffer,
• (e) a first mux connected to the scheduler and to the transport packet store,
• (f) a source of Null packets connected to the first mux,
• (g) means in response to the transport packet store being empty and there being at least one transport packet available for moving said one transport packet to the transport packet store,
• (h) said scheduler being operative to determine whether outputting the transport packet in the transport packet store will satisfy a first condition that it will not overflow the target buffer or a second condition that it will overflow the target buffer and signalling the first mux that the transport packet in the transport packet store will satisfy the first or the second condition,
• (i) said first mux being operative in response to the signalling from the scheduler of the first condition to select and read out the said transport packet from the transport packet store and output it and in response to the signalling from the scheduler of the second condition to select a Null packet from the Null packet source and output it,
• (j) packet restamping means connected to the clock means and connected to receive the transport packets outputted by the mux for re-stamping said transport packets with a new PCR value.