Compression denotes the techniques and protocols that reduce the bandwidth necessary for transmission of a given signal. For example, there is a huge amount of redundant information in the analogue audio and video signals. These can be removed and, consequently, the amount of bits per second that must be transmitted will be reduced substantially. Compression technologies determine the digital bandwidth by making a trade-off between how much capacity is available and the quality of service that is needed.
Compression standards have been a vital factor for enabling distribution of audio/video services on the IP networks. Furthermore, compression techniques are the main pillars in the digital broadcasting standards. A number of different standards are defined for audio/video compression. ITU, ETSI, and a number of other standardization organizations have been involved in the development of compression standards. Moving Pictures Expert Group (MPEG) has developed three audio/video compression standards, widely deployed in development of audio video services:
- MPEG-1. Primarily intended for applications like computer images and graphics.
- MPEG-2 is used in digital broadcasting. MPEG-2 is intended to be generic in the sense that it serves a wide range of applications, bit rates, resolutions and services. MPEG-2 covers different picture resolution from Low Level (352X288) pixels to a very high resolution of 1920X1152 pixels, also called High Definition TV (HDTV) resolution.
- MPEG-4. Contrary to the MPEG-1 and MPEG-2, which are frame-based, MPEG-4 is object-based. MPEG-4 supports two-dimensional arbitrarily shaped, natural video objects as well as synthetic data. Synthetic data includes text, generic 2D/3D graphics and animated faces, enabling content-based interaction and manipulation. MPEG-4 is an important standard for the distribution of Digital TV to Handheld devices, and also for broadband IPTV and Video on demand (VoD).