MOBI

From MobileRead

MOBI is the format used by the the MobiPocket Reader. It may have a .mobi extension or it may have a .prc extension. The extension can be changed by the user to either of the accepted forms. In either case it may be DRM protected or non-DRM. The .prc extension is used because the PalmOS doesn't support any file extensions except .prc and .pdb.

[edit] Description

MOBI format was originally an extension of the PalmDOC format by adding certain HTML like tags to the data. Many MOBI formatted documents still use this form. However there is also a high compression version of this file format that compresses data to a larger degree in a proprietary manner. There are some third party programs that can read the eBooks in the original MOBI format but there is no known third party program that can read the eBooks in the new compressed form. The higher compression mode is using a huffman coding scheme that has been called the Huff/cdic algorithm. For a description in python check huffdic.py available as part of the Calibre project.

From time to time features have been added to the format so new files may have problems if you try and read them with a down level reader. Currently the source files follow the guidelines in the Open eBook format.

[edit] MBP

This is the extension used on a side file (auxiliary) for MOBI formatted eBooks. It is used to store metadata used by the library software and also to store user entered data like bookmarks, annotations, last read position. This file is created automatically by the reader program when the eBook is first opened and has a .mbp extension. The Library management software in MobiPocket uses this file to get information displayed in the library window such as title and author so that it won't have to open the larger eBook file.

[edit] eBook Creation

There are several ways to create eBooks in the MOBI format. The rules for the format of the source files need to create eBooks in MOBI are spelled out in documents on the MobiPocket web site. The recommended tool called MobiPocket Creator is available as a download from the web site.

EBooks can also be converted from other forms using the Windows version of the MobiPocket Reader. Once converted the file can be used on any device supported by MobiPocket Reader.

[edit] Guidelines

In order to better support the features of the MobiPocket Reader there are some guidelines that need to be followed when creating a book in this format.

• Do not specify a default font family, font size or other font attributes such as weight or color. This is a choice the person reading the eBook should be able to make. Fonts Sizes and Attributes can be specified for special headings and other specific items. Use only generic font families.
• Do not impose justification for standard text. It may be needed for captions and other special text.
• Do not use tables for anything except table data. Nested tables are not supported.
• Do not use blank lines to try and force page changes. Use the <mbp:pagebreak/> tag.
• Do not use multiple books for different devices. Instead use advanced features such as multi resolution images and platform specific frames.

[edit] Adapting images to various PDA screen resolutions

The IMG tag in Mobipocket publications supports up to three source attributes for various resolutions: src, losrc and hisrc. This makes it possible to optimize the same ebook for various devices. The image to be displayed is dynamically selected by the Reader according to the resolution of the screen on the actual device:

Example:

<img hisrc="cover480x640.gif" src="cover220x300.gif" losrc="cover140x140.gif"/>

Please also notice that there is a 64KB internal limitation for images (this is a restriction of the Mobipocket .PRC format). GIFs have to be smaller than 64KB. You can use GIF optimization programs such as Ulead Smart Saver to get GIFs smaller than 64KB. (If images are bigger than 64KB, they are automatically resized to fit in the limit by MobiGEN but you might not like the result)

[edit] MOBI eBook Readers and converters

In addition to the readers supplied by MobiPocket there are also 3rd party readers and converters. This include:

• FBReader
• Book Designer
• MBP_reader (program that can extract MBP notes to text files).