From BlenderWiki
FBX Importing in Assimp
Basics
The actual FBX importing is implemented within assimp and follows the structure of the other Assimp importers. The following page in assimp's documentation
http://assimp.sourceforge.net/lib_html/extend.html
describes the process of adding a new importer very well (even though its outdated in some aspects).
Dealing with multiple FBX file format versions
The assimp importer will be taylored at reading ASCII fbx files in 2013 file format.
Rationale: 2013 is the newest format at the time of the writing and has thus the most features. Upgrading from lower format versions is easier (and causes less data loss) than downgrading. This way, users can use FBX converter to convert their files to 2013 format and no information will be lost (By the same logic, adding assimp support for older fbx formats should also be relatively easy.)
The FBX importer will check the input format version and decide whether the file can be imported or not.
Policy for dealing with older fbx versions
- If older format versions can be read using the same code and with no extra efforts (which should be the case for at least 2012, if not more!), accept them.
- Offer a 'strict mode' import flag. If set, do not accept older FBX files and hint users to use FBX converter. If the flag is not set, try your best at reading older files.
- 2011, 2012 and 2013 are almost identical and are definitely all supported. 2009 and earlier needs extra fixup code.
Binary files
Binary files map one-by-one to their ascii counterparts, it's just an encoding. Whle the initial focus is ASCII, the fbx importer is designed to be easily extended to support binary reading as well.
