The MOBI file format is one of the most widely used ebook file formats. The format is an enhancement to the old OEB (Open Ebook Format) format and was used as the proprietary format for Mobipocket Reader. Like EPUB, it is supported by almost all modern e-readers specifically by mobile devices with low bandwidth. The format can be converted to several other formats such as PDF, EPUB, and several other formats using publicly available software applications such as the Kindle app. There are several companies that offer free MOBI books such as Project Gutenberg, Feedbooks, and Open Library.
Amazon bought the company behind MOBI file format back in 2005. It was in 2011 when support for the MOBI file format was officially discontinued. Amazon’s current Kindle formats (AZW3, KF8 and KFX) are based on MOBI but have a different DRM scheme.
Features have been added to the format from time to time and new files may have problems if you try to read them with a down-level reader. The open eBook format is the present source to be followed by source files anyways.
MOBI File Format
Since MOBI is a proprietary file format, details about its format are not available publicly. It supports standard HTML and is one of the Open eBook Publication formats for eBook distribution.
MOBI file format has certain limitations as listed below.
Audio and Video contents are not supported
Images are not scalable with font size
Tables can be added individually and cannot be nested
Text can only have a hanging indent if it has no left margin
Blocks of text can never have a greater than normal margin on their right side