OMG Music

OMG Music is a "Music Context" that wraps the web browser's AudioContext.

Music created and shared in the OMG Music format contains information like key and time signatures that make the modification and mutation of beats and melodies simple.

It designed for the advancement of "open music", where music is shared in a "source code" format that promotes remixing.

This app supplies the core music functionality for the OMG Platform

OMG Song File Format

The song and its parts are a JSON file.

An overview of the file format looks like this:

 let song = {
      parts: [{name: "Piano", ...}],
      sections: [
           {
                name: "Verse",
                parts: [{name: "Piano", ...}]
           }
      ],
      beatParams: {...},
      keyParams: {...},
      name: "My Song"
 }

The song is separated "horizontally" into parts (such as piano, drums, guitar) and "vertically" into sections (such as Intro, Verse, Chorus).

The song.parts array is the part header, which contains information about how to make sounds from the part. This may contain a list of MP3 or WAV files contained in a Sound Set. Or a the part might generate sounds from Web Audio API's built in oscillators, or the WebAudioFont.

Each section in song.sections also has a parts array. This contains information about when to play each sound, producing a melody or a beat.

The parts in song.sections have either a notes array, or a tracks array.

notes Vs tracks

The notes array contains a list of objects that describe what note to play and for how long. Like this:

 notes = [
      {note: 0, scaledNote: 60, beats: 2.0},
      {rest: true, beats: 1.0},
      {note: 1, scaledNote: 62, beats: 1.0}
 ]

The scaledNote is a MIDI note determined from the key of the song and octave of the instrument of the part. In this case a middle C (MIDI note 60) is played for a two beats, then a one beat rest, then the D above it (MIDI note 62) is played for one beat.

The tracks array can contain multiple tracks (think bass drum, snare drum, high-hat). Each track is an array that contains an element for each subbeat in the current part. If the value N is a number between 0 and 1, the audio sample for that track is played at volume N. The entire audio sample is played.

Use notes when you need to determine how long an audio sample is played (such as in a melody or bassline).

Classes

THe main class is OMusicContext. This can load() songs or parts in the OMG format, or create blanks.

The OMGSong and OMGSongPart classes can be thought of as an "exo-skeleton" for the data. For example, the following data:

 let songData = {
      parts: [{name: "Piano", ...}],
      sections: [
           {
                name: "Verse",
                parts: [{name: "Piano", ...}]
           }
      ],
      beatParams: {...},
      keyParams: {...},
      name: "My Song"
 }

When loaded becomes:

 omgSong = {
      data: songData,
      parts: {
           "Piano: {data: partHeaderData}
      }
      Sections: {
           "Verse": {
                data: sectionData,
                parts: {
                     "Piano": {data: partDetailData}
                }
           }
      }
 }

The original songData still exists as omgSong.data. The parts and sections arrays of the data have been turned into objects/dictionaries. This is for easier access to parts and sections by name, which is useful when passing data through websockets and other layers.

All elements of songData can be accessed individually through these wrapper objects (OMGSong and OMGSongPart). The wrapper allows the player, and the context, and the user interfaces to attach temporary things which do not need to saved are cannot be stringified. For example, the GainNode for each part is on the OMGSongPart that wraps its the parts data.

These audio nodes needs to be associated with the part, but cannot be stringified, and need to be created for each session. So they go onto the wrapper.

Examples

Here are some apps where OMG Music is used:

• OpenMedia.Gallery social networking sites
• Dawesome (github)
• Techno GAUNTLET
• OMG Meme Maker
• Song Processor

Using the Client: Game Dev Example

How to: https://www.youtube.com/watch?v=TXpPFBkpXp0

(Note, the video has outdated code)

When the game is loading:

 import OMusicContext from "https://openmedia.gallery/apps/music/js/omusic.js"
 
 var music = new OMusicContext()
 var {song, player} = await music.load("http://openmusic.gallery/data/1333")

When the game starts:

 game.music.play()

Increase BPM and key when difficulty increases:

 music.beatParams.bpm += 20

 music.keyParams.rootNote++
 music.rescaleSong()

When the game ends:

 music.stop()