Definition of Terms - Digital Video and Audio Broadcasting Technology - page 560

and compression of video (Part 2) and audio (Part 3) to obtain an elemen-
tary stream, as well as the multiplexing of elementary streams to form a
transport stream (Part 1).
Multimedia Home Platform (MHP)
Program-associated DVB data service. HTML files and JAVA applica-
tions are broadcast via object carousels for MHP-enabled receivers and can
then be started in the receiver.
Multimedia and Hypermedia Information Group (MHEG)
Program-associated data service in MPEG-2 transport streams, based on
object carousels and HTML applications Broadcast in the UK as part of
DVB-T.
Network Information Table (NIT)
The NIT is a PSI table (MPEG-2/DVB). It comprises technical data
about the transmission network (eg orbit positions of satellites and trans-
ponder numbers). The NIT is transmitted in TS packets with PID 0x0010
and indicated by table_ID 0x40 or 0x41.
Null Packet
Null packets are TS packets with which the transport stream is filled to
obtain a specific data rate. Null packets do not contain any payload and
have the packet identity 0x1FFF. The continuity counter is undefined.
Orthogonal Frequency Division Multiplex (OFDM)
The modulation method is used in DVB systems for broadcasting trans-
port streams with terrestrial transmitters. It is a multicarrier method and is
suitable for the operation of single-frequency networks.
Packet Identity (PID)
The PID is a 13 bit value in the TS header. It shows that a TS packet be-
longs to a substream of the transport stream. A substream may contain a
packetized 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 the case of video streams one frame constitutes the PES,
whereas with audio streams, the PES is an audio frame which may repre-
sent an audio signal between 16 ms and 72 ms. Each PES packet is pre-
ceded 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 are pay-
load. With reference to an elementary stream (ES) only the useful data of
the ES without the PES header are payload.