Digital Video Broadcasting Technology
DVB System - Packetized elementary stream

The MPEG-2 multiplexer does not directly multiplex sequences of the access units from its inputs. All elementary streams consisting of the access units are transformed into so called packetized elementary streams (PES). Each PES consists of PES packets as can be seen in next Figure [21].

Principle of forming the packetized elementary stream

Every PES packet contains a header and a payload. The payload is a field where data of the original elementary stream are grouped in one after another. There is no limitation on synchronization of PES starts and access unit starts. That means a starting byte of the access unit can occupy any place (byte) of the PES packet payload. Several small-sized access units can even be put in the payload of one PES packet. PES packets can have a variable length but up to 64 kB in size. There is certain freedom for designers of the MPEG-2 multiplexer to utilize this flexibility. They can decide to apply PES packets of a fixed size or variable size to ensure that first byte of any PES packet payload will carry first byte of some access unit. Every PES packet header contains a start code (to identify a start of the PES packet), an identifier of stream (within programme), a length of the PES packet and its header, optional header subfields and flags (indicators of subfields).