Digital Video Broadcasting Technology
DVB System

DVB-S, DVB-T and DVB-C are best known as well as most used technologies for accessing the digital content. As was already mentioned, those standards define the physical and data link layer of an entire distribution system. All multimedia content is grouped and transmitted through MPEG transport streams (TS).

If we talk about the multimedia content namely its video and audio content it is good to realize that source video and audio signals are analog signals and they have to be converted into a digital form (analog-to-digital converter) to utilize benefits of a digitization. However, the analog video signal that needs a bandwidth of 5 MHz in case of a standard European 625-line TV signal with 720 pixels per line amounts to 414,720 (576 x 720) pixels per picture (frame). After digitization a black and white video signal (with 25 pictures per second) would require a rate of about 83 Mbps (or about 250 Mbps for color video). Those bit rates are too high and almost inapplicable in real communications (e.g. over satellite). Fortunately, video signals as well as audio signals contain a lot of redundant information that can be removed via suitable compression technique.

Using the compression the original rate can be decreased (based on quality and resolutions) to several Mbit/s. For this purpose the Moving Pictures Experts Group (MPEG) was formed with a task to develop efficient compression techniques for a work with moving clips in computers and their transport between computers or other devices. DVB technology adopted an MPEG-2 compression standard [20]. It supports several video qualities and resolutions as well as it provides high flexibility.

As was already said above DVB is set of standards covering not only video/audio compressing but all functions of an entire DVB system for digital video delivery to end users or other providers. Such DVB system has to multiplex all input streams (video, audio, data signals) into one final transport stream and send it via given transmission medium in a proper form. Next parts of this chapter will deal more with this stream processing.