The H.264 Advanced Video Compression Standard(second edtion) Chapter 1 学习摘要

Chapter 1  Introduction

1.1 a change of scene

Video compression or video encoding is the process of reducing the amount of data required
to represent a digital video signal, prior to transmission or storage. The complementary
operation, decompression or decoding, recovers a digital video signal from a compressed
representation, prior to display. Digital video data tends to take up a large amount of storage
or transmission capacity and so video encoding and decoding, or video coding, is essential for
any application in which storage capacity or transmission bandwidth is constrained.Almost
all consumer applications for digital video fall into this category, for example:

◦ Digital television broadcasting: TV programmes are coded prior to transmission over a
limited-bandwidth terrestrial, satellite or cable channel (Figure 1.1).
◦ Internet video streaming: Video is coded and stored on a server. The coded video is trans-
mitted (streamed) over the internet, decoded on a client and displayed (Figure 1.1).

◦ Mobile video streaming: As above, but the coded video is transmitted over a mobile network
such as GPRS or 3G (Figure 1.1).
◦ DVD video: Source video is coded and stored on a DVD or other storage medium. A DVD
player reads the disk and decodes video for display (Figure 1.1).
◦ Video calling: Each participant includes an encoder and a decoder (Figure 1.2). Video from
a camera is encoded and transmitted across a network, decoded and displayed. This occurs
in two directions simultaneously.
Each of these examples includes an encoder, which compresses or encodes an input video
signal into a coded bitstream, and a decoder, which decompresses or decodes the coded
bitstream to produce an output video signal. The encoder or decoder is often built in to a
device such as a video camera or a DVD player.

1.2 Driving the change

Effective video coding is an essential component of these applications and can make the difference between the suc-
cess or failure of a business model. Even though processor speeds and network bandwidths continue

to increase, a better video codec results in a better product and therefore a more competitive
product. This drive to improve video compression technology has led to significant investment
in video coding research and development over the last 15-20 years and to rapid, continuous
advances in the state of the art.

1.3 The role of standards

Standard-ized video coding formats have a number of potential benefits compared with non-standard,
proprietary formats:
r Standards simplify inter-operability between encoders and decoders from different manu-
facturers. This is important in applications where each ‘end’ of the system may be produced
by a different company, e.g. the company that records a DVD is typically not the same as
the company that manufactures a DVD player.
r Standards make it possible to build platforms that incorporate video, in which many different
applications such as video codecs, audio codecs, transport protocols, security and rights
management, interact in well-defined and consistent ways.
r Many video coding techniques are patented and therefore there is a risk that a particular
video codec implementation may infringe patent(s). The techniques and algorithms required
to implement a standard are well-defined and the cost of licensing patents that cover these
techniques, i.e. licensing the right to use the technology embodied in the patents, can be
clearly defined.

1.4 Why H.264 Advanced Video Coding is important

This book is about a standard, jointly published by the International Telecommunications
Union (ITU) and the International Standards Organisation (ISO) and known by several names:

‘H.264’, ‘MPEG-4 Part 10’ and ‘Advanced Video Coding’.

H.264/AVC is the latest in a series

of standards published by the ITU and ISO. It describes and defines a method of coding video
that can give better performance than any of the preceding standards. H.264 makes it possible
to compress video into a smaller space, which means that a compressed video clip takes up less
transmission bandwidth and/or less storage space compared to older codecs.

Better video compression is the key to delivering more, higher-quality video in
a cost effective way. H.264 compression makes it possible to transmit HD television over a
limited-capacity broadcast channel, to record hours of video on a Flash memory card and to
deliver massive numbers of video streams over an already busy internet.

H.264 has more options and parameters – more ‘control knobs’ – than any previous
standard codec. Getting the controls and parameters ‘right’ for a particular application is not
an easy task. Get it right and H.264 will deliver high compression performance; get it wrong
and the result is poor-quality pictures and/or poor bandwidth efficiency. Computationally ex-
pensive, an H.264 coder can lead to slow coding and decoding times or rapid battery drain on
handheld devices. Finally, H.264/AVC, whilst a published industry standard, is not free to use.