Ensemble Designs 4500 ASI and SMPTE 310M Converter and MPEG Transport Processor - Manual (Page 5)

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Model 4500 MPEG Stream Processor
Clock Quality and Transmission
This section addresses the underlying capabilities of the 4500. As background for that discussion, we
will take a quick look at the components of the transport stream.
The Transport Stream Hierarchy
The transport stream works as a hierarchy. At the top of the stream hierarchy is the PAT followed
by PID, PMT and PCR. See the following table for more information about the components of this
hierarchy.
Transport Stream Hierarchy
PAT Program Allocation Table
Goes by about every half a second; •
Shows how many programs are in the stream; •
Indicates which program it is; •
Points to the PID number or PMT for the program. •
PID Packet Identifier
PID number for program 1 is 100; PID number for program 2 is 312; •
In the PID stream, there will be a PAT every half a second; •
Every half second, there will be enough packets to add up to 19.3 Mb/s. •
PMT Program Map Table
Indicates how to find all constituent parts of the transport stream; •
Has description of the program; •
Indicates what the element count is; •
Refers to elemental streams that collectively make up the program; •
elemental stream includes video, audio, closed captions, surround sound;
Indicates where to find the PCR. •
PCR Program Clock Reference
An on-going set of packets; •
When used properly, the 4500 causes the PCR to be frequency and phase •
locked all the way back to the station.