Autodesk FBX Binary Specification

fbx_binary_specification.md

Autodesk FBX Binary Specification (unofficial)

Finding updated documentation on the binary format for FBX can be quite hard. After looking through various parsers from various open-source projects, I decided to write this short specification with the new and updated information I found.

NOTE: This is still a work in progress, although all values being shown should be correct.

Binary header

Size: 27 bytes

Offset (bytes)	Description	Value
0 - 20	File magic (string + 2 spaces + NULL terminator)	Kaydara FBX Binary \0
21	Unknown	0x1A (observed, might vary)
22	Endianness	0x00 = Little Endian, 0x01 = Big Endian
23 - 26	FBX Version (uint32)	Example: 7500

Property

Size: 25 + sizeof(name) + sizeof(Property[]) + sizeof(Node[])

Size (bytes)	Data type	Name
1	char	type_code
?	?	data

Type codes

Primitive types

Type code	Size (bytes)	Data type
Y	2	short
C	1	boolean (0 = false, 1 = true)
I	4	int
F	4	float
D	8	double
L	8	long

Array types

Type code	Size (bytes)	Data type
f	4 * array_length	float[]
d	8 * array_length	double[]
l	8 * array_length	long[]
i	4 * array_length	int[]
b	1 * array_length	boolean[] (0 = false, 1 = true)

Size (bytes)	Data type	Name
4	unsigned int	array_length
4	unsigned int	encoding
4	unsigned int	compressed_length
?	?	data

If encoding == 0, the data length is array_length * data type size. If encoding == 1, the data is a deflate/zip-compressed buffer of length compressed_length

Special types

Type code	Size (bytes)	Data type
S	1 * data_length	char[]
R	1 * data_length	unsigned byte[]

Size (bytes)	Data type	Name
4	unsigned int	data_length
?	char / unsigned byte	data

Node

FBX Version < 7500

Size: 25 + sizeof(name) + sizeof(Property[]) + sizeof(Node[])

Size (bytes)	Data type	Name
4	unsigned int	end_offset
4	unsigned int	property_count
4	unsigned int	property_len
1	unsigned byte	name_len
name_len	char[]	name
?	Property[]	properties
?	Node[]	children

FBX Version >= 7500

Size: 25 + sizeof(name) + sizeof(Property[]) + sizeof(Node[])

Size (bytes)	Data type	Name
8	unsigned long	end_offset
8	unsigned long	property_count
8	unsigned long	property_len
1	unsigned byte	name_len
name_len	char[]	name
?	Property[]	properties
?	Node[]	children

Credits

https://code.blender.org/2013/08/fbx-binary-file-format-specification/ https://github.com/FyroxEngine/Fyrox/blob/master/src/resource/fbx/document/binary.rs https://github.com/bqqbarbhg/ufbx/blob/master/ufbx.c