OTR File Format Specification

Overview

The OTR (Ocarina of Time Recompiled / Open Texture Resource) format is a custom archive format used to store game assets. It is primarily a ZIP archive containing individual asset files with specific binary headers.

Container Format

The .otr or .o2r file is a standard ZIP archive. Files inside the archive can be named arbitrarily, but typically follow a directory structure mirroring the original game's asset paths.

Asset Structure

Each file within the ZIP archive begins with a standard 64-byte header, followed by resource-specific data.

Standard Header (64 bytes)

Offset	Size	Type	Description
0x00	1	int8	Byte Order
0x01	1	bool	Is Custom Asset (0 = Original, 1 = Custom)
0x02	2	-	Padding
0x04	4	u32	Resource Type (Magic Number)
0x08	4	u32	Version
0x0C	8	u64	Unique Asset ID
0x14	44	-	Reserved / Padding

Note: All multi-byte integers are stored in Little Endian format.

Resource Types

The Resource Type field identifies the kind of data stored in the asset.

Magic Value	ASCII	Description
0x4F444C54	ODLT	[Display List](Display List Resource)
0x46669697	LGTS	[Light](Light Resource)
0x4F4D5458	OMTX	[Matrix](Matrix Resource)
0x4F464C54	OFLT	[Float](Float Resource)
0x56433346	VC3F	[Vec3f](Vector 3 Float Resource)
0x56433353	VC3S	[Vec3s](Vector 3 Short Resource)
0x4F424C42	OBLB	[Blob](Blob Resource)
0x4F544558	OTEX	[Texture](Texture Resource)
0x4F565458	OVTX	[Vertex](Vertex Resource)
0x4F565054	OVPT	[Viewport](Viewport Resource)
0x41415252	AARR	[Asset Array](Asset Array Resource)
0x47415252	GARR	[Generic Array](Generic Array Resource)