.FBX

Filmbox

Introduction

FBX began as the native format of Filmbox, a motion capture program by Kaydara that was later renamed MotionBuilder. Autodesk bought Kaydara in 2006 and FBX became the usual way to move models, skeletons and animation between Autodesk tools and game engines. The format is proprietary: Autodesk publishes an SDK for reading and writing it, not a specification.

FBX files are either binary, which is the usual form, or ASCII text.

Software

Structure

A binary FBX file begins with the text Kaydara FBX Binary, padded and ended with a zero byte, then two bytes and a 32-bit version number such as 7400. The rest is a tree of nodes. Each node record gives the offset where it ends, its number of properties, the length of its property list and its name, then its properties, then its child nodes. Properties are typed values: integers, floats, strings, raw bytes, or arrays of numbers, which may be zlib compressed. From version 7500 the offset and length fields grew from 32 to 64 bits.

The top-level nodes include FBXHeaderExtension, GlobalSettings, Definitions, Objects, which holds the geometry, models, materials and animation curves, and Connections, which links the objects into the scene.

  1. 0Magic Kaydara FBX Binary, zero byte, two bytes23 bytes
  2. 23Version unsigned 32-bit, for example 74004 bytes
  3. 27Nodes a tree of named records with typed propertiesvaries
    1. …Objects geometry, models, materials, animationvaries
    2. …Connections which object belongs to whichvaries
The outline of a binary FBX file.