Video Compression

Abstract

This document deals with the issues of video compression. The algorithm, which is used by the MPEG standards, will be elucidated upon in order to explain video compression. Only visual compression will be discussed (no audio compression). References and links to further readings will be provided in the text. What is compression? Compression is a reversible conversion (encoding) of data that contains fewer bits. This allows a more efficient storage and transmission of the data. The inverse process is called decompression (decoding). Software and hardware that can encode and decode are called decoders. Both combined form a codec and should not be confused with the terms data container or compression algorithms. Figure 1: Relation between codec, data containers and compression algorithms. Lossless compression allows a 100% recovery of the original data. It is usually used for text or executable files, where a loss of information is a major damage. These compression algorithms often use statistical information to reduce redundancies. Huffman-Coding [1] and Run Length Encoding [2] are two popular examples allowing high compression ratios depending on the data. Using lossy compression does not allow an exact recovery of the original data. Nevertheless it can be used for data, which is not very sensitive to losses and which contains a lot of redundancies, such as images, video or sound. Lossy compression allows higher compression ratios than lossless compression.