Digital Video Broadcasting Technology
DVB System - Elementary streams

The elementary streams can carry the MPEG-2 compressed video and audio, data, timing and system information, conditional access information and other programme related data. They represent components of the programme.

The simplest type of a programme is a radio service that consists of a single elementary audio stream. On the other hand a classical television service consists of three elementary streams: one stream carries coded video, second stream carries coded stereo audio and third contains teletext.

However, there is no problem to offer a television service containing one stream with video in the standard definition, one stream with high definition video, a several audio streams in different languages and even more streams for teletext in different languages [21].

Let’s consider an uncompressed digital video stream that consists of a sequence of frames. Each frame (e.g. 830 kB for 625 lines) representing an uncompressed video picture is called a presentation unit. MPEG-2 coder encodes and compresses every presentation unit making an access unit. The access units as can be seen in Figure below are not of the same size. Their size depends on original picture complexity and a type of each frame whether it is an I, P or B frame [20]:

An output of the MPEG-2 coder is a sequence of the access units and this sequence constitutes the elementary video stream. In the similar way an uncompressed audio stream of audio presentation units is encoded by the MPEG coder to a sequence of audio access units forming so the audio elementary stream.

Principle of video sequence coding