What is an .fbx file? Which version you have, and how to open it on a Mac

A whole scene in one file

STL or 3MF carry a model for printing. FBX carries a scene you keep working with in an animation package or a game engine:

• Geometry: polygon meshes, and NURBS surfaces too.
• Materials and textures. Textures can sit inside the file or next to it as separate images.
• Object hierarchy and skeletons – the bones a character moves on.
• Animation and deformers.
• Cameras and lights.
• Units and axis orientation of the scene.

That's why Maya, 3ds Max, MotionBuilder, Blender, Cinema 4D, Unreal Engine and Roblox Studio all use it. For 3D printing only the geometry matters, and not every slicer loads FBX.

A closed format since 1996

The Autodesk FBX SDK documentation says it plainly: "The FBX file format is not documented." Programs are meant to read and write FBX through the Autodesk FBX SDK. It's free, but under Autodesk's licence: not open source and not to be redistributed. In 2013 Blender published its own description of the binary encoding, worked out by reverse engineering.

The format came with Filmbox, motion-capture software from the Canadian company Kaydara. Filmbox was renamed MotionBuilder in 2002. Kaydara went to Alias (the deal was struck in 2004), and Autodesk bought Alias in January 2006. The origin still shows: every binary FBX begins with the words "Kaydara FBX Binary". And from 2003 there was a plug-in that let a Mac play FBX scenes in QuickTime Player; its last version came out in 2012.

Which FBX version you have

The version matters more than you'd think, because not every program reads every one. Terminal tells you the type and version:

head -c 18 model.fbx
od -An -t u4 -j 23 -N 4 model.fbx

For a binary file, the first command prints Kaydara FBX Binary; a text FBX starts with ; FBX. The second prints the binary file's version number, such as 7400 or 7500. Autodesk spells out what the numbers mean in the FBX SDK source itself:

Blender imports only binary FBX from version 7.1 on, and text FBX not at all. The Assimp library, which many programs use to read FBX – Preview3D among them – refuses files older than 7.1. It reads files newer than 7.4, just with a warning. A test file in version 7.5 opens in Preview3D without trouble. If a program refuses your FBX, check the version first.

Why an FBX opens without textures

Textures are often separate images next to the file. When they're embedded in the FBX, programs unpack them into a folder ending in .fbm when they open it. Either way, if you send only the .fbx, the textures are lost on the way. Send the whole folder, or zip the .fbx together with its images.

How to open FBX on a Mac, iPad and iPhone

macOS knows the FBX type but can't read it. Model I/O, the framework the system uses to open 3D files, doesn't load FBX, and Preview doesn't list it among its types (checked on macOS 27.0.1). So the Finder shows no preview and no thumbnail.

• [Autodesk FBX Review](https://apps.apple.com/us/app/fbx-review/id868956490) is free on the Mac App Store. According to the App Store, its last update was in March 2024.
• [Blender](https://www.blender.org/) is free and imports FBX as long as it's binary and version 7.1 or later. It is a full 3D package, though.
• Reality Converter from Apple can turn FBX into USDZ, but according to threads on the Apple Developer Forums only with Autodesk's FBX SDK installed.
• Preview3D, my app, opens FBX in its window, in Quick Look and as a Finder thumbnail. On iPad, iPhone and Apple Vision Pro too.

Preview3D reads FBX through Assimp, so the same version limits apply as above. It shows the geometry and basic materials; it doesn't play animation. Model info has the dimensions and triangle count, plus a mesh check (holes, flipped triangles, edges shared by more than two faces). On iPad and iPhone you can stand the model on your desk in AR.

Converting FBX to STL or OBJ

On a Mac, Preview3D converts from File → Export model as… (⌥⌘E) to STL, OBJ or PLY, without uploading anything. Bones, animation, cameras and lights are dropped, and STL carries no colours or textures either.

Common questions

Is FBX an open format?

No. It belongs to Autodesk, which doesn't publish how it's written. The official route is the Autodesk FBX SDK.

Why does Blender say ASCII FBX isn't supported?

Blender imports only binary FBX. Save the file again as binary in the program it came from.

How do I find out the FBX version?

In Terminal, with od -An -t u4 -j 23 -N 4 model.fbx. It prints something like 7400, which is FBX from Autodesk's 2014 and 2015 products.

Why did my FBX open without textures?

The textures aren't in the file itself but next to it, or in an .fbm folder. Move them together with the .fbx.

Can I 3D print an FBX?

Convert it to STL or 3MF first. Not every slicer loads FBX, and for printing you only need the geometry anyway.

Does Preview on a Mac open FBX?

No, not even on macOS 27. The system knows the type but can't read it.

Related pages

• The .stl file – the printing format FBX is most often converted to
• The .3mf file – a mesh with units and colours

Sources

• Library of Congress: FBX – history, SDK licence, what the format carries
• PRONOM: binary FBX and ASCII FBX – how a file begins
• Autodesk FBX SDK: fbxio.h – versions and product years
• Autodesk FBX SDK: the format is not documented
• Blender: binary FBX specification (2013)
• Assimp 6.0.5: FBX version check
• Blender: error importing ASCII FBX
• Apple Developer Forums: Reality Converter and the FBX SDK

Have an FBX you couldn't open on your Mac? Write to me at apps@xfanta.com with the program and version it came from.