Professional PHP4 Multimedia Programming is an extremely handy book to have on your bookshelf, even if (and possibly especially if) you don't design and implement multimedia applications with PHP all the time. Within hours of getting the book, I realized that I could use PHP as a commandline scripting language to solve several problems. I've used it as a reference several times since, even though I do NOT consider myself a PHP Multimedia Applications developer.
The book is organized nicely. As a "Professional" book, it assumes a decent understanding of PHP. This assumption saves you lots of time and unnecessary hand holding. There is a brief PHP refresher chapter for those who aren't quite as familiar with PHP as necessary, but after that refresher chapter, you're expected to understand things. You bought this book (or will, anyway) because you already know how to program in PHP but are not familiar with the various multimedia extensions.
The next several chapters each dedicate themselves to a specific extension concept: Ming, Ming with ActionScript, GD, ImageMagick, PDFLib, and FDF.
Each chapter gives an overview of the library, it's uses and limitations, and gives lots of example source code giving examples of all the functions in an extension and how they are used together.
The next few chapters are full-fledged application case studies. Though you may not agree with the authors' coding styles, these case studies walk you through (from start to finish) several different applications to show you how the libraries can be used within the scope of a larger PHP application, not just example toy scripts.
Following the case studies are several appendices. Each appendix is a language reference for a multimedia extension. Most of the information in the appendices is found online in the PHP manual, and I, for one, find it more convenient to look it up there, but having it in the book is a nice bonus.
Another wonderful addition is a full-color screenshots gallery index, which shows you what various scripts from within the chapters should look like when run. This is great for two reasons: 1) You can "check your work" as you write the applications and sample code in the book, and 2) You can see the results of functions in the book while reading it away from the computer.
I would definitely recommend this book to anyone who is thinking about writing even just ONE application in PHP that will manipulate any supported multimedia (Shockwave, images, PDF/FDF, etc.) The time you save by having this book as a companion will more than pay for the cost of the book.