/midi-soundfont-sidecarfile-specification

Primary LanguageHTMLGNU General Public License v3.0GPL-3.0

Abstract

A simple, implicit method for media players, DAWs and midisequencers, to automatically load soundfont files when playing score files (.mid e.g.), enhancing the playback experience without requiring user configuration.

MIDI Soundfont Sidecar specification

  • Level: 0
  • Version: 0.5
  1. Sidecar File Detection:
  • Primary: Media players SHOULD first look for a soundfont sidecar file (=with the exact same name) as the MIDI file (excluding the file extension).
  • Fallback: If a soundfont file is not detected, media players SHOULD then look for other soundfont sidecar files with the same naming convention

Fallback order: .SF2 > .SF3 > .SFZ > .DLS

NOTE: a mediaplayer-engine does not have to support all soundfont-fileformats to be spec-compliant. Supporting the lowest common denominator (.SF2 in 2025) is enough.

  1. Example

Here’s a fictional music-album, based on midi- and soundfont-files:

$ cd album 
$ ls

drwxr-xr-x   2 leon users  4096 Jun 20 21:39 .
drwxrwxrwt 295 root root  94208 Jun 20 21:39 ..
-rw-r--r--   1 leon users   200 Jun 20 21:38 song1.mid
-rw-r--r--   1 leon user  10000 Jun 20 21:38 song1.sf2
-rw-r--r--   1 leon users   200 Jun 20 21:38 song2.mid
lrwxrwxrwx   1 leon users     9 Jun 20 21:39 song2.sf2 -> song1.sf2

$ mediaplayer song1.mid

the mediaplayer will scan for the soundfont in the same directory (song1.sf2 e.g.), and use that instead of the global configured soundfont.

  1. File Naming Convention:
  • The sidecar file MUST have the same name as the MIDI file, differing only by the file extension (.DLS or .SF2 e.g.).
  • Example:
    • mysong.mid → mysong.SF2 (primary) or mysong.SFZ (fallback e.g.)

Soundfont file-extensions are case-insensitive (valid: .sf2 or .SF2 or .Sf2 e.g.)

  1. Playback Behavior:
  • Upon finding a matching sidecar file, the media player SHOULD load the soundfont from this file for the duration of the MIDI file playback.
  • If no sidecar file is found, the media player SHOULD fall back to its default soundfont or configured soundfont settings.
  • symlinked (or windows junctioned) soundfonts should be allowed (to preserve space)

In case of online players: HTTP HEAD requests can be used to check for soundfont-sidecar-files.

  1. Implementation Notes:
  • This spec is designed to be lightweight and easy to implement, encouraging broad adoption across various media players and platforms.
  • Implementors are encouraged to provide an option for users to override this behavior if desired (e.g., always using a default soundfont, disabling sidecar loading).
  1. Relation to RMIDI and Other Formats:
  • This specification might serve as an ‘override’ feature for RMIDI files, allowing users to play RMID content with a custom soundfont without having re-encoding of the RMID file.
  • It is format-agnostic, meaning it can be applied to various MIDI file formats beyond RMID.

Adoption and Feedback:

  • Implementors and interested parties are invited to provide feedback and suggestions for future revisions.
  • A list of adopting media players and software will be maintained to track the spec’s ecosystem impact.

Revision History:

  • v0.5: Initial release.

Next Steps:

  1. Review and Feedback: Circulate this draft among the mentioned projects (VLC-player, fluidsynth, etc.) and relevant communities for feedback.
  2. Revision (if necessary): Based on the feedback received, revise the spec to better meet the needs of implementors and users.
  3. Publication and Promotion: Publish the finalized spec on a dedicated webpage or within relevant developer resources, and promote it across music tech, developer, and open-source communities.
  • leonvankammen|isvery.ninja

IANA Considerations

This document has no IANA actions.

Acknowledgments

TODO acknowledge.