An Introduction to Video Coding

David R. Bull,    Bristol Vision Institute, University of Bristol, Bristol BS8 1UB, UK

Abstract

Visual information is the primary consumer of communications bandwidth across all broadcast, internet, and mobile networks. Users are demanding increased video quality, increased quantities of video content, more extensive access, and better reliability. This is creating a major tension between the available capacity per user in the network and the bit rates required to transmit video content at the desired quality. Network operators, content creators, and service providers therefore are all seeking better ways to transmit the highest quality video at the lowest bit rate, something that can only be achieved through video compression.

This chapter provides an introduction to some of the most common image and video compression methods in use today and sets the scene for the rest of the contributions in later chapters. It first explains, in the context of a range of video applications, why compression is needed and what compression ratios are required. It then examines the basic video compression architecture, using the ubiquitous hybrid, block-based motion compensated codec. Finally it briefly examines why standards are so important in supporting interoperability.

This chapter, necessarily only provides an overview of video coding algorithms, and the reader if referred to Ref. [1] for a more comprehensive description of the methods used in today’s compression systems.

Keywords

Image compression; Video compression; Video applications; Discrete cosine transform; Entropy coding; Motion estimation; Video standards

Nomenclature

1-D one dimensional

2-D two dimensional

3-D three dimensional

AC alternating current. Used to denote all transform coefficients except the zero frequency coefficient

ADSL asymmetric digital subscriber line

ASP advanced simple profile (of MPEG-4)

AVC advanced video codec (H.264)

B bi-coded picture

bpp bits per pixel

bps bits per second

CCIR international radio consultative committee (now ITU)

CIF common intermediate format

codec encoder and decoder

CT computerized tomography

CTU coding tree unit

CU coding unit

DC direct current. Refers to zero frequency transform coefficient.

DCT discrete cosine transform

DFD displaced frame difference

DFT discrete Fourier transform

DPCM differential pulse code modulation

DVB digital video broadcasting

EBU European Broadcasting Union

FD frame difference

fps frames per second

GOB group of blocks

GOP group of pictures

HDTV high definition television

HEVC high efficiency video codec (H.265)

HVS human visual system

I intra coded picture

IEC International Electrotechnical Commission

IEEE Institute of Electrical and Electronic Engineers

IP internet protocol

ISDN integrated services digital network

ISO International Standards Organization

ITU International Telecommunications Union. -R Radio; -T Telecommunications

JPEG Joint Photographic Experts Group

kbps kilobits per second

LTE long term evolution (4G mobile radio technology)

MB macroblock

mbps mega bits per second

MC motion compensation

MCP motion compensated prediction

ME motion estimation

MEC motion estimation and compensation

MPEG Motion Picture Experts Group

MRI magnetic resonance imaging

MV motion vector

P predicted picture

PSNR peak signal to noise ratio

QAM quadrature amplitude modulation

QCIF quarter CIF resolution

QPSK quadrature phase shift keying

RGB red, green, and blue color primaries

SG study group (of ITU)

SMPTE Society of Motion Picture and Television Engineers

TV television

UHDTV ultra high definition television

UMTS universal mobile telecommunications system

VDSL very high bit rate digital subscriber line

VLC variable length coding

VLD variable length decoding

YCbCr color coordinate system comprising luminance, Y, and two chrominance channels, Cb and Cr

5.01.1 Introduction

Visual information is the primary consumer of communications bandwidth across all broadcast, internet, and mobile networks. Users are demanding increased video quality, increased quantities of video content, more extensive access, and better reliability. This is creating a major tension between the available capacity per user in the network and the bit rates required to transmit video content at the desired quality. Network operators, content creators, and service providers therefore are all seeking better ways to transmit the highest quality video at the lowest bit rate, something that can only be achieved through video compression.

This chapter provides an introduction to some of the most common image and video compression methods in use today and sets the scene for the rest of the contributions in later chapters. It first explains, in the context of a range of video applications, why compression is needed and what compression ratios are required. It then examines the basic video compression architecture, using the ubiquitous hybrid, block-based motion compensated codec. Finally it briefly examines why standards are so important in supporting interoperability.

This chapter, necessarily only provides an overview of video coding algorithms, and the reader if referred to Ref. [1] for a more comprehensive description of the methods used in today’s compression systems.

5.01.2 Applications areas for video coding

By 2020 it is predicted that the number of network-connected devices will reach 1000 times the world’s population; there will be 7 trillion connected devices for 7 billion people [2]. Cisco predict [3] that this will result in 1.3 zettabytes of global internet traffic in 2016, with over 80% of this being video traffic. This explosion in video technology and the associated demand for video content are driven by:

5.01.2.1 Markets for video technology

A huge and increasing number of applications rely on video technology. These include:

5.01.2.1.1 Consumer video

Entertainment, personal communications, and social interaction provide the primary applications in consumer video, and these will dominate the video landscape of the future. There has, for example, been a massive increase in the consumption and sharing of content on mobile devices and this is likely to be the major driver over the coming years. The key drivers in this sector are: