Introduction to Digital TV Transmission Technique
MTD200 MPEG Test Decoder User Manual
1–9
The individual elementary streams contain time stamps, such as the Decoding
Time Stamps (DTS) and the Presentation Time Stamps (PTS), for synchronizing
the decoding and display of the individual elementary streams. The Packetized
Elementary streams (PES) are transmitted in packets with up to a length of
64 kBytes (more for video streams), which define a certain display length (e.g., a
picture in case of video streams). A header precedes each packet of an elementa-
ry stream (PES). The header also contains the DTS and PTS. If a transport
packet contains the beginning of a PES packet, the 10th bit (Payload Unit Start
Indicator) is set in the header of the transport packet.
The PTS / DTS value (33 bit) corresponds to the state of a 90 kHz counter and
refers to the 33 most significant bits of the PCR. The ratio of 27 MHz (PCR) to
90 kHz (PTS / DTS) is 300 and is attained by the fact that the 9 least significant
bits of PCR only count to 300 (instead of 512).
Two different time stamps (DTS and PTS) are provided, since the order of arrival
of the PES packets and their decoding does not always correspond to the order of
display (for instance during the transmission of difference pictures in video
streams). In many cases, only one PTS is available.
The tables defined by the DVB project (see ETS 300 468) are to be seen as
service information. The information contained in these tables is not required for
decoding, but provides convenient access for the end user: it might be program
information for the viewer or control information for the decoder and units
connected to it.
In many cases, PSI (Program Specific Information) is also mentioned in
connection with SI (Service Information). PSI is already defined in MPEG-2 and
contains the above-mentioned tables PAT (Program Association Table), PMT
(Program Map Table), CAT (Conditional Access Table), and NIT (Network
Information Table). The latter contains data provided by the network operator for
tuning the receivers (for example, orbit positions or transponder numbers). The
CAT and NIT contents are specified by the DVB project (and not by MPEG).
Tables additionally defined by the DVB project are as follows:
BAT (Bouquet Association Table) contains information about the different
programs of a broadcaster irrespective of their propagation paths.
SDT (Service Description Table) describes the programs offered.
EIT (Event Information table) supplies the data base for an electronic TV
guide with information about the type of program and age classification for
the viewer.
RST (Running Status Table) contains status information about the individual
programs and especially serves for controlling video recorders.
Service Information
Summary of Contents for MTD200
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