DRO

DOSBox Raw OPL or DRO is the format used by DOSBox to capture OPL output. The format uses a clear header but went through two incompatible versions. The first version was used up to DOSBox 0.72, the second version replaced it starting with DOSBox 0.73.

Technical information

All numerical values are little-endian.

Offset	Size	Description
0	char[8]	Signature (must be DBRAWOPL)
8	uint16	First version word
10	uint16	Second version word

Version number identification is complicated by the fact the version words aren't read in the same order depending on the specifications. In the 1.0 version of the format, the minor version number comes first, and the major version number is the second word. So for version 1.0, the value is 00 00 01 00. However, version 2.0 of the specifications reverse the order, so for version 2.0, the value is 02 00 00 00. For this reason, the 1.0 version also became known as version 0.1.

Note: Some files using the old version format contain large garbage values in the minor version word. ZDoom will refuse to read them. You will need to set the minor version to 00 00 with a hex editor.

Delay values are indicated in milliseconds - 1. Since a delay of 0 is deemed to be useless, the byte value is increased by one to get the actual delay.

The header is then followed by a subheader. The two different formats have completely different subheaders.

Format 1.0

Size	Description
12	uint32	Song length (in millisecond)
16	uint32	Song data size (in bytes)
20	uint8	Hardware type (0: OPL2, 1: OPL3, 2: Dual OPL2)
21	byte[3]	Optional null padding (may not be present: if non-null, these bytes are song data)

Format 2.0

Size	Description
12	uint32	Song data size (in pairs of bytes)
16	uint32	Song data length (in milliseconds)
20	uint8	Hardware type (0: OPL2, 1: Dual OPL2, 2: OPL3)
21	uint8	Data format (ZDoom only supports data format 0)
22	uint8	Compression method (ZDoom only supports compression 0, meaning no compression)
23	uint8	Short delay code (command value used to introduce a one-byte delay, should always be 122)
24	uint8	Long delay code (command value used to introduce a one-byte delay multiplied by 256, should always be 123)
25	uint8	Codemap table size (must be 126 or less, technically should always be 122)
26	uint8*	Codemap table (associate OPL registers with index values)

The standard codemap looks like this:

Index	Register		Index	Register		Index	Register		Index	Register		Index	Register		Index	Register		Index	Register		Index	Register
0	01		1	04		2	05		3	08		4	BD		5	20		6	40		7	60
8	80		9	E0		10	21		11	41		12	61		13	81		14	E1		15	22
16	42		17	62		18	82		19	E2		20	23		21	43		22	63		23	83
24	E3		25	24		26	44		27	64		28	84		29	E4		30	25		31	45
32	65		33	85		34	E5		35	28		36	48		37	68		38	88		39	E8
40	29		41	49		42	69		43	89		44	E9		45	2A		46	4A		47	6A
48	8A		49	EA		50	2B		51	4B		52	6B		53	8B		54	EB		55	2C
56	4C		57	6C		58	8C		59	EC		60	2D		61	4D		62	6D		63	8D
64	ED		65	30		66	50		67	70		68	90		69	F0		70	31		71	51
72	71		73	91		74	F1		75	32		76	52		77	72		78	92		79	F2
80	33		81	53		82	73		83	93		84	F3		85	34		86	54		87	74
88	94		89	F4		90	35		91	55		92	75		93	95		94	F5		95	A0
96	B0		97	C0		98	A1		99	B1		100	C1		101	A2		102	B2		103	C2
104	A3		105	B3		106	C3		107	A4		108	B4		109	C4		110	A5		111	B5
112	C5		113	A6		114	B6		115	C6		116	A7		117	B7		118	C7		119	A8
120	B8		121	C8		122	short delay								123	long delay

External links

• DRO Format on the Shikadi DOS Game Modding Wiki
• DRO on the Videogame Music Preservation Foundation Wiki
• Modland repository of DRO files