H.264与MPEG-4视频压缩技术解析

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"H.264_and_MPEG-4_Video_Compression.pdf" 该资源是一本关于视频编解码技术的书籍，特别关注H.264和MPEG-4这两种编码标准。这本书由Iain E.G. Richardson撰写，适合视频处理领域的初学者，它深入浅出地解释了视频编码的基本原理和技术，同时也涵盖了实际应用中的标准细节。书中讨论的关键知识点包括： 1. **离散余弦变换（DCT）**：DCT是视频压缩中用于将像素数据转换到频率域的重要工具，它可以高效地去除空间冗余，将能量集中在低频部分，从而实现数据压缩。 2. **运动估计（ME）**：运动估计是视频编码中的关键步骤，它通过寻找最佳匹配块来估计帧间像素的运动，从而减少连续帧之间的相似信息，实现时间冗余的消除。 3. **变长编码（VLC）**：VLC是一种高效的编码方式，根据符号出现的概率分配不同的位数，频繁出现的符号用较少的位表示，不常见的符号则用更多的位表示，这样可以进一步压缩数据。 4. **去块滤波（Deblocking）**：由于熵编码可能导致块效应，去块滤波器在解码后对图像进行平滑处理，以减少视觉上不连续的块状结构，提高图像质量。 5. **H.264编码标准**：H.264，也称为AVC（Advanced Video Coding），是目前广泛使用的视频编码标准之一，以其高效率和优质图像而闻名。它采用了更复杂的运动补偿、多参考帧、熵编码优化以及高级预测模式，从而实现了比MPEG-4更高的压缩比。 6. **MPEG-4编码标准**：MPEG-4是另一种国际标准，强调了对象编码和交互性，允许用户操作视频中的单个对象，支持高级交互功能和多媒体集成。 7. **下一代多媒体视频编码**：书中的“Video Coding for Next-generation Multimedia”暗示了作者还探讨了未来视频编码的发展趋势，可能包括高效视频编码（HEVC）、AV1等新技术。通过这本书，读者不仅可以理解视频编码的基本原理，还能了解到H.264和MPEG-4的实际应用，这对于从事视频编解码工作的专业人士或对这个领域感兴趣的学生来说是非常有价值的资源。同时，它提醒我们尊重版权，合法使用和分享知识。

Foreword

Work on the emerging “Advanced Video Coding” standard now known as ITU-T Recom-

mendation H.264 and as ISO/IEC 14496 (MPEG-4) Part 10 has dominated the video coding

standardization community for roughly the past three years. The work has been stimulating,

intense, dynamic, and all consuming for those of us most deeply involved in its design. The

time has arrived to see what has been accomplished.

Although not a direct participant, Dr Richardson was able to develop a high-quality,

up-to-date, introductory description and analysis of the new standard. The timeliness of this

book is remarkable, as the standard itself has only just been completed.

The new H.264/AVC standard is designed to provide a technical solution appropriate

for a broad range of applications, including:

Broadcast over cable, satellite, cable modem, DSL, terrestrial.

Interactive or serial storage on optical and magnetic storage devices, DVD, etc.

Conversational services over ISDN, Ethernet, LAN, DSL, wireless and mobile networks,

modems.

Video-on-demand or multimedia streaming services over cable modem, DSL, ISDN, LAN,

wireless networks.

Multimedia messaging services over DSL, ISDN.

The range of bit rates and picture sizes supported by H.264/AVC is correspondingly broad,

addressing video coding capabilities ranging from very low bit rate, low frame rate, “postage

stamp” resolution video for mobile and dial-up devices, through to entertainment-quality

standard-deﬁnition television services, HDTV, and beyond. A ﬂexible system interface for the

coded video is speciﬁed to enable the adaptation of video content for use over this full variety

of network and channel-type environments. However, at the same time, the technical design

is highly focused on providing the two limited goals of high coding efﬁciency and robustness

to network environments for conventional rectangular-picture camera-view video content.

Some potentially-interesting (but currently non-mainstream) features were deliberately left out

(at least from the ﬁrst version of the standard) because of that focus (such as support of

arbitrarily-shaped video objects, some forms of bit rate scalability, 4:2:2 and 4:4:4 chroma

formats, and color sampling accuracies exceeding eight bits per color component).

Foreword

•

xvi

In the work on the new H.264/AVC standard, a number of relatively new technical

developments have been adopted. For increased coding efﬁciency, these include improved

prediction design aspects as follows:

Variable block-size motion compensation with small block sizes,

Quarter-sample accuracy for motion compensation,

Motion vectors over picture boundaries,

Multiple reference picture motion compensation,

Decoupling of referencing order from display order,

Decoupling of picture representation methods from the ability to use a picture for reference,

Weighted prediction,

Improved “skipped” and “direct” motion inference,

Directional spatial prediction for intra coding, and

In-the-loop deblocking ﬁltering.

In addition to improved prediction methods, other aspects of the design were also enhanced

for improved coding efﬁciency, including:

Small block-size transform,

Hierarchical block transform,

Short word-length transform,

Exact-match transform,

Arithmetic entropy coding, and

Context-adaptive entropy coding.

And for robustness to data errors/losses and ﬂexibility for operation over a variety of network

environments, some key design aspects include:

Parameter set structure,

NAL unit syntax structure,

Flexible slice size,

Flexible macroblock ordering,

Arbitrary slice ordering,

Redundant pictures,

Data partitioning, and

SP/SI synchronization switching pictures.

Prior to the H.264/AVC project, the big recent video coding activity was the MPEG-4 Part 2

(Visual) coding standard. That speciﬁcation introduced a new degree of creativity and ﬂex-

ibility to the capabilities of the representation of digital visual content, especially with its

coding of video “objects”, its scalability features, extended N-bit sample precision and 4:4:4

color format capabilities, and its handling of synthetic visual scenes. It introduced a number

of design variations (called “proﬁles” and currently numbering 19 in all) for a wide variety

of applications. The H.264/AVC project (with only 3 proﬁles) returns to the narrower and

more traditional focus on efﬁcient compression of generic camera-shot rectangular video pic-

tures with robustness to network losses – making no attempt to cover the ambitious breadth of

MPEG-4 Visual. MPEG-4 Visual, while not quite as “hot off the press”, establishes a landmark

in recent technology development, and its capabilities are yet to be fully explored.

Foreword

•

xvii

Most people ﬁrst learn about a standard in publications other than the standard itself.

My personal belief is that if you want to know about a standard, you should also obtain a

copy of it, read it, and refer to that document alone as the ultimate authority on its content,

its boundaries, and its capabilities. No tutorial or overview presentation will provide all of the

insights that can be obtained from careful analysis of the standard itself.

At the same time, no standardized speciﬁcation document (at least for video coding), can

be a complete substitute for a good technical book on the subject. Standards speciﬁcations are

written primarily to be precise, consistent, complete, and correct and not to be particularly

readable. Standards tend to leave out information that is not absolutely necessary to comply

with them. Many people ﬁnd it surprising, for example, that video coding standards say almost

nothing about how an encoder works or how one should be designed. In fact an encoder is

essentially allowed to do anything that produces bits that can be correctly decoded, regardless

of what picture quality comes out of that decoding process. People, however, can usually only

understand the principles of video coding if they think from the perspective of the encoder, and

nearly all textbooks (including this one) approach the subject from the encoding perspective.

A good book, such as this one, will tell you why a design is the way it is and how to make

use of that design, while a good standard may only tell you exactly what it is and abruptly

(deliberately) stop right there.

In the case of H.264/AVC or MPEG-4 Visual, it is highly advisable for those new to the

subject to read some introductory overviews such as this one, and even to get a copy of an

older and simpler standard such as H.261 or MPEG-1 and try to understand that ﬁrst. The

principles of digital video codec design are not too complicated, and haven’t really changed

much over the years – but those basic principles have been wrapped in layer-upon-layer of

technical enhancements to the point that the simple and straightforward concepts that lie at

their core can become obscured. The entire H.261 speciﬁcation was only 25 pages long, and

only 17 of those pages were actually required to fully specify the technology that now lies at

the heart of all subsequent video coding standards. In contrast, the H.264/AVC and MPEG-4

Visual and speciﬁcations are more than 250 and 500 pages long, respectively, with a high

density of technical detail (despite completely leaving out key information such as how to

encode video using their formats). They each contain areas that are difﬁcult even for experts

to fully comprehend and appreciate.

Dr Richardson’s book is not a completely exhaustive treatment of the subject. However,

his approach is highly informative and provides a good initial understanding of the key con-

cepts, and his approach is conceptually superior (and in some aspects more objective) to other

treatments of video coding publications. This and the remarkable timeliness of the subject

matter make this book a strong contribution to the technical literature of our community.

Gary J. Sullivan

Biography of Gary J. Sullivan, PhD

Gary J. Sullivan is the chairman of the Joint Video Team (JVT) for the development of the latest

international video coding standard known as H.264/AVC, which was recently completed as a

joint project between the ITU-T video coding experts group (VCEG) and the ISO/IEC moving

picture experts group (MPEG).

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