====== NSPC File Format ======

NSPC is a file format used by Herringway's [[https://github.com/Herringway/nspcplay|nspcplay]] designed to contain all the data necessary to play music from Nintendo's Kankichi-kun/N-SPC music format.

===== Structure =====
An NSPC file contains a simple header, followed by a number of variable-length audio packs, followed by optional FIR coefficient tables and [[https://mutagen-specs.readthedocs.io/en/latest/apev2/apev2.html|APEv2 tags]]. At minimum, an NSPC file is expected to contain a single sequence, instruments, BRR sample data and a sample directory.

===== Header =====

The header is 32 bytes long.

^ Offset ^ Size ^ Purpose          ^ Description                                                       ^
| 0      | 4    | Variant          | Identifies the variant of NSPC. See valid identifiers below.      |
| 4      | 2    | Sequence address | The SPC700 address that the song's sequence data is loaded to.    |
| 6      | 2    | Instrument table | The SPC700 address that the song's instrument table is loaded to. |
| 8      | 2    | Sample directory | The SPC700 address where the BRR samples are expected to be found.|
| 10     | 1    | Release table    | The id of the release table to use.                               |
| 11     | 1    | Volume table     | The id of the volume table to use.                                |
| 12     | 19   | Variant-specific | Variant-specific data. See variant information for details.       |
| 31     | 1    | FIR coefficients | Number of FIR coefficients embedded in file. If 0, use defaults.  |

===== Audio Pack Format =====
An audio pack is a chunk of binary data, prefixed with two 16-bit unsigned integers. Size, followed by length, followed by length bytes of binary data. The last pack MUST have a 16-bit null terminator immediately following it.

===== FIR Coefficient Table =====
This is a chunk of binary data, with a byte length equal to the FIR coefficient table length times eight.

===== Variants =====

==== 0 - Standard ====
This is the most common variant. The unmodified Kankichi-kun supplied to game developers uses this format.

==== 1 - Prototype ====
This is an early version of variant 0, used in early SNES games like Super Mario World.

==== 2 - Konami ====
This is a heavily modified variant 0, with several changed commands. Details are largely unknown.

==== 3 - AddMusicK ====
This is an upgraded version of variant 0, with many new commands. Designed for use in Super Mario World ROM hacks.

===== TODO =====
  * Find out if any link exists between Metroid II's music driver and NSPC. They are suspiciously similar.
  * Document the commands unique to each variant