Chapter 17. Compression of Digital Voice and Video

This chapter looks at a new advanced topic: multimedia networking . This important topic requires a thorough understanding of the process of preparing compressed voice and video. A raw piece of information, whether voice or video, must be converted to digital form and then compressed to save link bandwidth. This chapter discusses methods of preparing digital voice and video for multimedia networks, including the analysis of information sources, source coding, and limits of data compression. Typical voice and video streaming compression techniques, such as JPEG, MPEG, and MP3, are explained. The major topics of this chapter are

• Overview of data compression

• Digital voice and compression

• Still images and JPEG compression

• Moving images and MPEG compression

• Limits of compression with loss

• Compression process without loss

• Case study: FAX compression for transmission

Our discussion starts with an overview of data preparation and compression, focusing on voice, image, and moving-image data. Considerable effort is required to turn analog voice into digital form. This process of converting from raw voice to compressed binary formsampling, quantization, and encodingis known as pulse code modulation (PCM).

We then take a quick look at some practical compression methods without loss. We review the compression schemes that are used after the binary voice or image is prepared. We discuss both JPEG and MPEG compression techniques for still images and moving images, respectively. Still images or moving images might contain redundant or repeated elements that can be eliminated and codes substituted for future decoding process. We also summarize Shannon's limits of compression with loss. At the end of the discussion on compression, we review lossless compression techniques, such as Huffman encoding and run-length encoding . The chapter ends with a case study on FAX compression for transmission.