Tektronix MTD200, Руководство пользователя

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Glossary
MTD200 MPEG Test Decoder User Manual
Glossary–5
Packet Identity (PID)
The PID is a 13–bit value in the TS header. It shows that a TS packet belongs
to a substream of the transport stream. A substream may contain a packe-
tized elementary stream (PES), user–specific data, program specific
information (PSI) or service information (SI). For some PSI and SI tables the
associated PID values are predefined (see 1.3.6.). All other PID values are
defined in the PSI tables of the transport stream.
Packetized Elementary Stream (PES)
For transmission, the ”continuous” elementary stream is subdivided into
packets. In case of video streams one picture constitutes the PES, whereas
with audio streams an audio frame which may represent an audio signal
between 16 ms and 72 ms is the PES. Each PES packet is preceded by a PES
header.
Payload
Payload signifies useful data in general. With reference to the transport
stream all data except for the TS header and the adaptation field is payload.
With reference to an elementary stream (ES) only the useful data of the
corresponding ES without the PES–header is payload.
Payload Unit Start Indicator
The payload unit start indicator is a 1–bit flag in the second byte of a TS
header. It indicates the beginning of a PES packet or of a section of PSI or SI
tables in the corresponding TS packet.
PCMCIA
PCMCIA is a physical interface standardized by the Personal Computer
Memory Card International Association for the data exchange between
computers and peripherals. A model of this interface is used for the common
interface.
PCR Jitter
The value of a PCR exactly refers to the beginning of a TS packet in which it
is located. The reference to the 27–MHz system clock yields an accuracy of
approx. 20 ns. If the difference of the transferred values deviates from the
actual difference of the beginning of the corresponding packets, this is called
a PCR jitter. It can be caused, for example, by an inaccurate PCR calculation
during transport stream multiplexing or by the subsequent integration of
null packets on the transmission path without PCR correction.