Apple’s iBooks textbooks for iPad stakes a position against openness in e-book publishing.
The format of the books is not a standard EPub format. The only tool that can create this format is Apple’s iBooks Author, and the only application that can view it is iBooks. An article on Ars Technica reports that it uses “ePub 2 along with certain HTML5 and JavaScript-based extensions that Apple uses to enable multimedia and interactive features. Those interactive features will only work with Apple’s iBooks app, not with other e-reader software or hardware, because only Apple supports those extensions.”
A post on Glazblog (the author says he’s “Co-chairman of the W3C CSS Working Group”; it would be nice if he gave his name) gives technical details. It uses XML namespaces that aren’t publicly documented, a nonstandard MIME type, and a private CSS extension.
This means you can’t view the books on anything but iOS. If Apple ever drops support for the format, it’s obsolete and impossible to support.
On top of this, the EULA for iBooks Author restricts sale of books created with it to the Apple Store. You can give away your books by any channel you like, but if you sell them, you must use the Apple Store. This means that if Apple doesn’t accept your book for publication, you can’t sell it in that format. (Except maybe in France, as Glazblog amusingly notes.) This is like having a compiler that lets you create software which you may sell only through Petitmol, or a video application that forbids you from selling your movies through anyone but FooTube. I can’t think of a precedent for this.
Authors normally would like to be able to take a book to a different publisher if their previous one loses interest. With books created with iBooks Author, you can’t do that, for both technical and legal reasons. The format isn’t under DRM, though, and the exclusivity applies to the format, not the content. As far as I can tell, you should be able to extract most of the content and republish it in a different format.
Apple’s restrictions make iBooks textbooks unsuitable for assignment to classes, unless the school is willing to give every student an iPad. Those who use other devices would be left out in the cold.
Apart from the restrictions, does Apple’s new format offer anything exciting? My own reaction, from briefly looking at a few sample books on a co-worker’s iPad, is that the interactive graphics are attention-getting, but the most important form of “interactivity” with a textbook is trying things out on your own — playing with the equations, writing sentences in the language, whatever. The best accessory for that is still a pencil and paper.
Mad File Format Science 
Making sense of MPEG audio formats
Lately I’ve been trying to clarify in my mind exactly how certain common MPEG-related audio formats are defined. I think I’ve got this right, but if anyone can offer corrections, they’d be appreciated.
MP3
This is the common name for MPEG-1 and MPEG-2, Audio Layer 3, which defines an encoding method. The difference between the MPEG-1 and MPEG-2 variants is just in the sampling rates. It’s audio-only. An “MP3 file” is normally a raw MP3 stream without a container.
MP4
MP4 means MPEG-4 Part 14. This is a container format which can hold audio, video, or both. It doesn’t specify the encoding method. In principle you could have an MP3 stream in an MP4 file. The preferred extension for MP4 containers is .mp4, but many others are used to denote specific encodings within MP4 containers.
AAC
This is short for MPEG-2 Part 7, Advanced Audio Coding. MPEG-4, Part 7 defines some extensions of it. That’s the encoding; several different containers may be called “AAC files” if they hold an AAC stream. A raw AAC stream file is possible but not common. MP4 is the most common container, so “MP4 audio” and “AAC” are often treated as if they were synonyms. HE-AAC, also known as aacPlus, is an MPEG-4 audio profile. HE-AAC decoders can decode AAC, but not vice versa.
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