BAND package

Apple publishes no specification. Its guide says only that a project is “a package (with a .band file extension)”. Anyone copying one to a non-Apple device or service should compress it first, since it is really a folder. The layouts below are those recorded on the MultimediaWiki page for GarageBand.

Layouts by version

Older versions

Song.band/
  projectData
  Media/                       the source AIFF files

The earliest layout recorded.

GarageBand 6 or thereabouts

Song.band/
  projectData
  Contents/
    PkgInfo
  Media/
    Images/
    Recording/
  Output/
    arrange_screenshot.tiff
    metadata.plist
    Output.aif
  Thumbs/

A layout the wiki dates tentatively to April 2014.

GarageBand 10.0.3 (October 2014)

Song.band/
  projectData
  Alternatives/
    000/
      Autosave/
      DisplayState.plist
      MetaData.plist
      Previews/
        Output.aif
      ProjectData
      Undo Data.nosync/
      WindowImage.jpg
  Contents/
    PkgInfo
  Media/
    Audio Files/
    Freeze Files.nosync/
  Output/
    Output.aif
  Resources/
    ProjectInformation.plist

The layout with alternatives.

This is the same shape as a Logic Pro package, and Logic Pro opens GarageBand projects, but no public source found confirms that their ProjectData and property lists match Logic’s in detail.

The files

File or folder	Holds
`projectData`	In the layouts recorded, XML with a large block of base64 data inside its data tags. Decoded, the data is binary with readable strings mixed in, such as instrument names.
`Alternatives/000/ProjectData`	A binary project file, recorded by name only in the 10.0.3 layout
`Alternatives/000/MetaData.plist`, `DisplayState.plist`	Property lists; contents not recorded for GarageBand
`Media/`	The project’s audio: `Audio Files/`, `Recording/` and `Images/` in the layouts above
`Media/Freeze Files.nosync/`	Frozen tracks, as AIFF files
`Output/Output.aif`, `Alternatives/000/Previews/Output.aif`	A mix of the song, for previews
`Output/metadata.plist`	Metadata; contents not recorded
`Contents/PkgInfo`	The package marker file of a macOS bundle
`Resources/ProjectInformation.plist`	Project information

Not confirmed

Whether later versions of GarageBand still write these layouts.
The contents of projectData and ProjectData beyond the XML wrapper above, and the keys of the property lists.
The exact GarageBand versions the older two layouts belong to.