byaml.md

Misc > Binary YAML

These files are similar to regular YAML files, but are encoded in binary form. They usually have the file extension .byml or .byaml.

A BYAML file contains a graph of nodes. Every node has a type and value. There are sequence types, such as arrays and dictionaries, and basic types such as strings and integers. The root node must always be an array or dictionary.

BYAML files are used to store all kinds of data, such as configuration data and levels.

Note: a BYAML file may contain cycles. This means that an array or dictionary may contain a node that the parser has seen earlier. Because of this, parsers must be careful not to end up in an infinite loop.

Header

In most games, the header looks as follows:

Offset	Size	Description
0x0	2	Magic number / BOM (BY: big endian, YB: little endian)
0x2	2	Version number
0x4	4	Offset to dictionary key table
0x8	4	Offset to string table
0xC	4	Offset to root node (array or dictionary)

Only in Mario Kart 8, an additional binary data table is used:

Offset	Size	Description
0x0	2	Magic number / BOM (BY: big endian, YB: little endian)
0x2	2	Version number
0x4	4	Offset to dictionary key table
0x8	4	Offset to string table
0xC	4	Offset to binary data table
0x10	4	Offset to root node (array or dictionary)

If a table is empty, the offest in the header is 0.

Changelog

Version	Changes
v1	Initial file format.
v2	Unsigned integers were added (0xD3).
v3	64-bit values were added (0xD4 - 0xD6).
v4	Binary data was added again (0xA1), but without binary data table (0xC3).
v5	Binary data with param (0xA2) was added.
v6 or v7	Hashmaps (0x20 - 0x3F) and ordered dictionaries (0xC4) were added.
v8 to v10	Unknown

Node Types

ID	Type	Version
0x20 ‑ 0x2F	Hash map	(6 or 7)+
0x30 ‑ 0x3F	Ordered hash map	(6 or 7)+
0xA0	String	Any
0xA1	Binary data	4+ and MK8
0xA2	Binary data with param	5+
0xC0	Array	Any
0xC1	Dictionary	Any
0xC4	Ordered dictionary	(6 or 7)+
0xD0	Bool	Any
0xD1	Integer	Any
0xD2	Float	Any
0xD3	Unsigned integer	2+
0xD4	Integer (64 bits)	3+
0xD5	Unsigned integer (64 bits)	3+
0xD6	Double	3+
0xFF	Null	Any

The following node types may not be contained in an array or dictionary. They are only used by the header:

ID	Type	Version
0xC2	String table	Any
0xC3	Binary data table	MK8

Node Values

To store values, arrays and dictionaries reserve 32 bits per element. Because not all node types fit into 32 bits, they are stored as follows:

Type	Value
0xA0	An index into the string table (see header).
0xA1	An absolute offset to a binary blob. The blob is prefixed by a 32-bit integer that holds its size. MK8 stores an index into the binary data table instead (see header).
0xA2	An absolute offset to a binary blob. The blob is prefixed by a 32-bit integer that holds its size and another 32-bit integer with application-specific information.
0xC0 ‑ 0xC4	An absolute offset to the node.
0xD0 ‑ 0xD3	Simply the value.
0xD4 ‑ 0xD6	An absolute offset to the value.
0xFF	Doesn't matter, always 0.

Array

If the number of elements is not a multiple of 4, additional null bytes are inserted between the type table and the data table such that the data table is aligned to 4 bytes.

Offset	Size	Description
0x0	1	Node type (0xC0)
0x1	3	Number of elements (N)
0x4	N	Type table
	4 x N	Value table

The type table contains one byte per element that indicates its node type. The format of a value depends on the node type (see here).

Dictionary

A dictionary contains key / value pairs. The pairs must be sorted by their keys, because a binary search algorithm is used to look them up.

Offset	Size	Description
0x0	1	Node type (0xC1)
0x1	3	Number of element (N)
0x4	8 x N	Element table

Every element is stored as follows:

Offset	Size	Description
0x0	3	Index into dictionary key table (see header)
0x3	1	Node type
0x4	4	Value

String Table

Offset	Size	Description
0x0	1	Node type (0xC2)
0x1	3	Number of strings (N)
0x4	4 x (N + 1)	Address table
		Null-terminated strings

The address table contains offsets to the strings, relative to the start of the string table node. It also contains an offset that points to the end of the string table (right behind the last string).

The address table and strings must both be sorted, because a binary search algorithm is used to find them.

Binary Data Table

Offset	Size	Description
0x0	1	Node type (0xC3)
0x1	3	Number of binary blobs (N)
0x4	4 x (N + 1)	Address table
		Binary data

The address table contains offsets to the binary data, relative to the start of the binary table node. It also contains an offset that points to the end of the binary table (right behind the last binary blob).

The address table must be sorted, because the size of a binary blob is calculated from the difference between two offsets.

Ordered Dictionary

Dictionary elements are always stored in alphabetical order. To restore the original order, ordered dictionaries store an array of indices behind the element table.

Offset	Size	Description
0x0	1	Node type (0xC4)
0x1	3	Number of elements (N)
0x4	8 x N	Element table
		Index table

Every element is stored as follows:

Offset	Size	Description
0x0	3	Index into dictionary key table (see header)
0x3	1	Node type
0x4	4	Value

The index table contains a list of indices into the element table. The size of each index depends on the number of elements (N):

• If there are less than 256 elements, the index table contains one byte per element.
• If there are less than 65536 elements, the index table contains two bytes per element.
• Otherwise, the index table contains 4 bytes per element.