bemusepack — Packs BMS files into .bemuse archive

BMS files need to be converted into .bemuse file format before playing on BE☆MU☆SE. It is a simple file format to hold BMS files and keysound files together. A custom format is created to be easily consumed by web applications, both on desktop and mobile devices.

File Format Specification

A .bemuse file contains

• an arbitrary metadata
• an opaque payload

Usually, the metadata describes what's inside the payload.

File Format

• 10 bytes magic string BEMUSEPACK
• 4 bytes Uint32LE — metadata size N (may be 0 if no metadata)
• N bytes — metadata
• the rest of the file — payload

Metadata

An entry file should have a metadata of more than 0 bytes. It should be a valid JSON. It describe all files both internal and external. External packages should have metadata of 0 bytes.

{
  version: 2,
  song: { title, artist, genre, ... },
  refs: [
    { size, hash }, // the first ref (0) describes its own payload
    { path, size, hash }, // ref 1's payload metadata
    ...
  ],
  files: [
    {
      name, type, size, hash,
      refs: [
        [ ref, start, end ], // start, end relative to payload
        ...
      ]
    }
  ]
}