Writing MIDI Files¶

Below is a basic guide to writing .mid and .rmi files.

Writing a MIDI file¶

writeMIDI¶

Writes the sequence as a Standard MIDI File.

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midi.writeMIDI();

The returned value is an ArrayBuffer - a binary representation of the Standard MIDI File.

Example¶

Below is a basic example of writing a modified MIDI file

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// create your midi and synthesizer
const midi = BasicMIDI.fromArrayBuffer(yourBufferGoesHere);
const synth = new SpessaSynthProcessor(44100);

// ...

// get the snapshot and apply it
const snapshot = synth.getSnapshot();
midi.applySnapshot(snapshot);

// write midi
const midiBinary = midi.writeMIDI();

// save the file
const blob = new Blob([midiBinary.buffer], { type: "audio/midi" });
const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = midi.name + ".mid";
a.click();

Writing an .rmi file¶

writeRMIDI¶

This function writes out an RMIDI file (MIDI + SF2). See more info about this format

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const rmidiBinary = midi.writeRMIDI(soundBankBinary, configuration);

The method is called on a BasicMIDI instance; that instance is the MIDI file to embed.

Parameters¶

soundBankBinary¶

ArrayBuffer - The binary sound bank (SF2 or DLS) to embed into the file.

configuration¶

Object, optional - A partial options object. All properties are optional.

• bankOffset - number - The bank offset to apply to the file. Default 0. See this for more info

• soundBank - BasicSoundBank - The sound bank instance that soundBankBinary contains. Used for correcting bank and program changes when correctBankOffset is enabled. If omitted, bank correction may be less accurate.

• correctBankOffset - boolean - If the function should correct all program-selects and bank-selects in the MIDI file to reflect the embedded sound bank (i.e., make it self-contained). Recommended unless a specific use-case is required. Default true.

• metadata - Object - The metadata of the file. If left undefined, some basic metadata (like the song's title) will be copied from the MIDI.

• name - string - the name of the song.
• engineer - string - the engineer of the sound bank.
• artist - string - the artist of the song.
• album - string - the album's name.
• genre - string - the song's genre.
• comment - string - a comment about the song.
• creationDate - Date - the creation date of the file. If not provided, current day is used.
• copyright - string - the copyright string. If not provided, midi.getExtraMetadata() is used.
• picture - ArrayBuffer - the album cover of the song. Binary data of the image.
• midiEncoding - string - The encoding of the inner MIDI file. Make sure to pick a value acceptable by TextDecoder.

Example¶

Below is a simple example for exporting an RMIDI file

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<label for="soundfont_upload">Upload soundfont</label>
<input type="file" id="soundfont_upload" />
<label for="midi_upload">Upload MIDI</label>
<input type="file" id="midi_upload" />
<button id="export">Export</button>

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const sfInput = document.getElementById("soundfont_upload");
const midiInput = document.getElementById("midi_upload");
document.getElementById("export").onchange = async () => {
    // get the files
    const soundBank = SoundBankLoader.fromArrayBuffer(
        await sfInput.files[0].arrayBuffer()
    );
    const midi = BasicMIDI.fromArrayBuffer(
        await midiInput.files[0].arrayBuffer()
    );

    // trim the soundfont
    soundBank.trim(midi);
    // write out with compression to save space (0.5 is medium quality)
    await soundBank.setSampleFormat({
        format: "compressed",
        compressionFunction: SampleEncodingFunction // Remember to get your compression function
    });
    const soundfontBinary = soundBank.writeSF2();
    // get the rmidi
    const rmidiBinary = midi.writeRMIDI(soundfontBinary, {
        soundBank,
        metadata: {
            name: "A cool song",
            artist: "John",
            creationDate: new Date(),
            album: "John's songs",
            genre: "Rock",
            comment: "My favorite!"
        }
    });

    // save the file
    const blob = new Blob([rmidiBinary.buffer], { type: "audio/rmid" });
    const url = URL.createObjectURL(blob);
    const a = document.createElement("a");
    a.href = url;
    a.download = midi.name + ".rmi";
    a.click();
};