iOS音视频开发实战指南：Mac与iOS音频编程详解

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"《Learning Core Audio：Mac和iOS音频编程实践指南》是一本针对iOS音视频开发的专业书籍，作者是Chris Adamson和Kevin Avila。这本书旨在提供深入且实践导向的学习，帮助读者掌握Core Audio框架，它是Apple在Mac和iOS平台上进行音频处理的核心技术。Core Audio是苹果系统中的音频基础设施，负责管理音频输入、输出和处理，包括音频流的调度、混音和播放。本书的重要内容包括但不限于以下几个方面： 1. 入门与基础：首先介绍Core Audio的基本概念，如音频数据流、音频设备接口（I/O）和音频单元（AU），帮助读者建立起对音频处理的系统理解。 2. 实战项目：书中提供了丰富的实例和项目，让学习者通过编写代码实现实际的音频功能，如创建音效、实时处理音频信号、连接外部硬件等，提升编程技能。 3. 跨平台支持：由于涵盖了Mac和iOS，读者可以了解到如何在不同的操作系统环境下管理和优化音频性能，确保应用程序的兼容性和用户体验。 4. 高级特性：深入探讨了诸如多通道音频、MIDI、音频路由和网络音频传输等高级主题，帮助开发者应对复杂音频应用场景。 5. 调试与性能优化：书中还涉及了音频编程中的常见问题解决策略，以及如何通过工具和技术来分析和优化音频应用的性能。 6. 实用技巧：分享了音频编程中的最佳实践，如内存管理、线程同步和资源释放，确保代码的健壮性。《Learning Core Audio》适合那些希望在iOS音视频开发领域深入学习和实践的开发者，无论是初学者还是有经验的工程师，都能从中获得宝贵的知识和技能。通过阅读这本书，读者将能够构建出高质量、高效的音频应用程序，满足用户对音频体验的期待。"

About the Authors

Chris Adamson is an independent writer, editor, and developer who lives in Grand

Rapids, Michigan. Now focusing on iOS and Mac development, he is the coauthor of

iOS SDK Development (Pragmatic Programmers, 2012). He is also the author of

QuickTime for Java: A Developer’s Notebook (O’Reilly Media, 2005) and coauthor of Swing

Hacks (O’Reilly Media, 2005). He was formerly the editor of java.net and ONJava.com.

He consults and publishes through his corporate identity, Subsequently and Furthermore,

Inc., with a focus on user-facing and digital media development for Mac and iOS. He

blogs on digital media software development at www.subfurther.com/blog. In a previous

career, he was a writer/associate producer at CNN Headline News, and over the years, he

has managed to own 11 1/2 Macs.

Kevin Avila (a.k.a. dogbert) is a smooth blend of carbon compounds, oxygen, hydrogen,

and nitrogen, with some impurities for added flavor. Additionally, he has more than 15 years’

experience developing for the Mac and, since its release, the iPhone. Kevin has been

involved in every corner of the audio market, from being an engineer at Apple to con-

figuring professional recording studios. He currently is a code mercenary for various

clients while he sits in his underwear at home, sipping coffee.

Foreword

Reflect for a minute on your craft.Think of those in ages past who shared the same

experiences.Think of the painters who drove themselves mad trying to gather the forces

within to produce something of meaning.Think of the industrialists, who believed they

were standing at the dawn of a new age, one that they themselves were capable of

building.

Think of the ancient acolytes of magic, seeking to unlock the power in arcane

knowledge.Then think of that moment when, having learned street magic tricks such as

flow control and data structures, you finally gained access to the API libraries. Think of

that sorcerer’s apprentice staring glassy-eyed at the universe of possibilities in a room of

musty books.

It’s one of those key moments in any programmer’s career, cresting that foothill only

to see the mountain beyond. It is the daunting realization that programming is a lifelong

journey of learning. Many would-be magicians simply turn around and head back out

the door, leaving that world behind to pursue a more normal life of sane pursuits.

That you have found your way here suggests you are part of the other group, a select

few blessed with some genetic predisposition to solving hard problems.They are the

ones who cross that threshold and enter that world, losing themselves to learning new

spells and exploring new kinds of magic.

For what is programming but magic? Wielding secret words to command powerful

forces you just barely understand, calling forth the spirits of bygone spell casters to ease

your burdens, simplify your workflows, and grant you the ability to surprise and delight

the masses.

As you pore over each tome, practicing new forms of magic, you start combining

them with the things you learned before creating new spells, thus unlocking new possi-

bilities. Everything you learn leads to new tricks to learn, new roads forking into other

new roads, until one day you run into a dead end.

Many of the ancient texts refer to such dark arts as audio programming but do not

deal with them directly. As vital as Core Audio is, there seem to be no books on the sub-

ject, no scrolls of spells or sample code to practice.There are plenty of use cases for audio

programming, but as black magic, the only materials you can find to read about it are

terse and confusing.

Chris Adamson tracked down a practitioner of the audio arts named Kevin Avila, a

graying wizard well versed in C.Through a combination of bribery and honest inquiry,

he established himself as a protégé.The rabbit hole he entered goes on forever, and as his

xvi

Foreword

ears led him through its many dark twists and turns, he learned a new language to

describe sound—and, with it, a new way of looking at the universe.

An eternity later, he himself a graying wizard, he thought back on that library to the

missing volumes and realized it was his destiny to shed light on the dark art of Core

Audio. It is the definition of mastery that we must teach what we have learned.This is

the truth that fuels the cycle of master and protégé.This is the engine that drives genera-

tions forward, each propelling the next further ahead as we move toward that grand inef-

fable vanishing point we call the future.

As with all rites of passage, it was a herculean task, requiring a whole new sets of skills

and a different type of discipline.We must tear apart our knowledge, and ourselves, to

find not just truth, but the beauty that underlies the truth and allows it to resonate across

the ages and to be understood.

All such that at some unknowable time in the future, where once there was a dead

end and a blank space between Core Animation and Core Data, some young acolyte

might find wisdom and guidance.They might combine this new knowledge with what

they already know so that, when they find their own dead end and their own dark arts,

they, too, will be ready.

That moment, dear reader, is now.That acolyte is you, and the grimoire that you hold

in your hand has all the wisdom and more than enough spells to take your magic to the

next level.This book is your key to wielding unspeakable power, the power of sound and

nature, the power of Core Audio.

Does all that seem a bit much for a book about audio programming? Rest assured

that, if anything, I have undersold it. Sound is an incredibly powerful force that affects

the human brain in ways we only barely understand. Consider the impact of music on

your life. Now consider that all of music is maybe 10% of the story of sound.

The power of audio programming goes so far beyond anything you can experience

with your ears. Swiping a credit card used to require an expensive machine. Now you

can do the same trick with a cheap plastic dongle plugged into the headphone jack of

your iPhone.You don’t have to make music to make magic with sound.

With this book, you dig into your first Core Audio code in Chapter 1, “Overview of

Core Audio,” even as you are learning what exactly Core Audio is and when you should

(and should not) attempt to use its power.

Core Audio, like all black arts, has roots in the inherent properties of nature. Chapter

2,“The Story of Sound,” takes to heart the story of sound, not as ineffable natural phe-

nomena, but as simple science.You’ll learn the language and techniques of converting

vibrating air molecules into the mathematical language of computers, and vice versa.

Yo u ’ l l a l s o l e a r n t h e h u m a n l a n g u a g e o f a u d i o a n d t h e real meanings of technical

terms you’ve heard, and perhaps even used, for years: sample rate, frame rate, buffer, and

compression.You’ll see these ideas carried through Chapter 3,“Audio Processing with

Core Audio,” as you peel back the wrapper on audio formats and learn about the canon-

ical formats Core Audio uses internally.

When you know the basics of Core Audio, you’ll want to apply your skills by learn-

ing the parlor tricks of recording and playback with Chapters 4, “Recording,” and 5,

“Playback,” using the high-level Audio Queue architecture.

Of course,“high-level” can be a misnomer, especially if you’re coming from an

object-oriented background such as Cocoa. Setting aside the comforting warmth of

Objective-C to take the reins of C can certainly be scary, but with a little understanding,

you’ll come to see how much like Cocoa a C framework can be, as familiar friends, like

key-value pairs, emerge in unfamiliar clothes.

When you understand Audio Queues, you’ll be a master of audio formats—almost.

First you must complete your quest by learning to convert between formats and come to

understand the relevance of canonical formats.

Then it’s time to say goodbye to high-level shores as you strap on your diving suit

and descend into the depths of Core Audio, the modular Audio Units that implement

the magic. Chapters 7,“Audio Units: Generators, Effects, and Rendering,” and 8,“Audio

Units: Input and Mixing,” will make or break you as an audio programmer, for here you

can craft end-to-end sonic solutions that are not possible “the easy way.”

Once time is your plaything, it’s time to tackle space. In Chapter 9, “Positional

Sound,” you enter another dimension as you learn to change sounds by positioning

audio in space using OpenAL, the 3D audio framework.

Core Audio has its roots in the Mac but has evolved with Apple’s fortunes. In Chapter

10,“Core Audio on iOS,” you focus on iOS and the challenges and changes brought by

the post-PC world of ultraportable hardware running ultra-efficient software.

Mobile hardware is not the only way to take audio beyond the computer. In Chapter

11,“Core MIDI,” you gain the means to connect the computer to musical instruments

and other hardware using Core Audio’s implementation of the industry-standard Musical

Instrument Digital Interface, Core MIDI.

With that, you’ll be at the end of your quest, but your journey will have just begun.

In Chapter 12,“Coda,” you look to the future, to the once inexplicable advanced con-

cepts you are now equipped to tackle, such as digital signal processing and sampling.

If you want to be a master of the arcane arts, you have a long road ahead of you.

There’s no sense sugarcoating it:This is going to be hard. But don’t worry—you’re in

good hands.Your authors have used plain language and plenty of sample code to banish

the demons and show you the way to the underlying logic that will make these concepts

yours.

Core Audio is the most powerful system for audio programming man has yet to cre-

ate, but its power has largely remained out of the hands of most app makers and locked

in the brains of audio nerds like Kevin. Chris has done what nobody else has managed

to do and may never manage to do again: Explain Core Audio in a way other people can

understand.

This book has been years in the making, and it took an incredible amount of work

and the best tech editor in the industry, the legendary Chuck Toporek, and his talented

colleagues at Pearson to finally bring it into existence.The people into whose waiting

xvii

Foreword

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