Initial commit
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王新升
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import { Midi } from '@tonejs/midi'
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import { writeMidi } from 'midi-file'
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import type { MidiData, MidiEvent } from 'midi-file'
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import type { NoteEvent, ProjectSnapshot, TimeSignature } from '../types'
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const DEFAULT_SIGNATURE: TimeSignature = [4, 4]
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// Decode UTF-8 byte string (latin1 encoded) to proper Unicode string
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// This matches: text.encode("latin1").decode("utf-8") in Python
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function decodeUtf8ByteString(byteString: string): string {
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try {
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const bytes = new Uint8Array(byteString.length)
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for (let i = 0; i < byteString.length; i++) {
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bytes[i] = byteString.charCodeAt(i)
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}
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return new TextDecoder('utf-8').decode(bytes)
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} catch {
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return byteString
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}
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}
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// Encode Unicode string to UTF-8 byte string (latin1 encoding)
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// This matches: text.encode("utf-8").decode("latin1") in Python
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function encodeUtf8ByteString(text: string): string {
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const bytes = new TextEncoder().encode(text)
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let output = ''
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bytes.forEach((b) => {
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output += String.fromCharCode(b)
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})
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return output
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}
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export async function importMidiFile(file: File): Promise<ProjectSnapshot> {
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const buffer = await file.arrayBuffer()
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return parseMidiBuffer(buffer)
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}
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export async function parseMidiBuffer(buffer: ArrayBuffer): Promise<ProjectSnapshot> {
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const midi = new Midi(buffer)
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const tempo = midi.header.tempos[0]?.bpm ?? 120
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const timeSignature = (midi.header.timeSignatures[0]?.timeSignature as TimeSignature | undefined) ?? DEFAULT_SIGNATURE
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// Merge notes from all tracks and sort by ticks then by midi (for stable ordering)
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const allNotes = midi.tracks
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.flatMap(t => t.notes)
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.sort((a, b) => a.ticks - b.ticks || a.midi - b.midi)
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// Get lyrics from header.meta and sort by ticks
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const lyricEvents = midi.header.meta
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.filter((event) => event.type === 'lyrics')
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.sort((a, b) => a.ticks - b.ticks)
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// Match lyrics to notes by tick position
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// Each lyric should be consumed by exactly one note at the same tick
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const lyricsByTick = new Map<number, string[]>()
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for (const event of lyricEvents) {
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const existing = lyricsByTick.get(event.ticks) || []
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existing.push(decodeUtf8ByteString(event.text))
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lyricsByTick.set(event.ticks, existing)
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}
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// Track which lyrics have been used at each tick position
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const usedLyricIndices = new Map<number, number>()
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const notes: NoteEvent[] = allNotes.map((note, index) => {
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const beat = note.ticks / midi.header.ppq
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const durationBeats = note.durationTicks / midi.header.ppq
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let lyric = ''
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// First try exact tick match
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const lyricsAtTick = lyricsByTick.get(note.ticks)
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if (lyricsAtTick && lyricsAtTick.length > 0) {
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const usedIndex = usedLyricIndices.get(note.ticks) || 0
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if (usedIndex < lyricsAtTick.length) {
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lyric = lyricsAtTick[usedIndex]
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usedLyricIndices.set(note.ticks, usedIndex + 1)
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}
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}
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// If no exact match, try nearby ticks (within small tolerance)
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if (!lyric) {
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const tolerance = midi.header.ppq / 100 // Very small tolerance
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for (const [tick, lyrics] of lyricsByTick.entries()) {
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if (Math.abs(tick - note.ticks) <= tolerance) {
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const usedIndex = usedLyricIndices.get(tick) || 0
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if (usedIndex < lyrics.length) {
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lyric = lyrics[usedIndex]
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usedLyricIndices.set(tick, usedIndex + 1)
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break
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}
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}
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}
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}
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return {
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id: `${index}-${note.midi}-${Math.round(note.ticks)}`,
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midi: note.midi,
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start: beat,
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duration: Math.max(durationBeats, 0.0625),
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velocity: note.velocity,
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lyric,
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}
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})
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return { tempo, timeSignature, notes, ppq: midi.header.ppq }
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}
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// Used to add absoluteTime property for sorting
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type WithAbsoluteTime<T> = T & { absoluteTime: number }
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export function exportMidi(snapshot: ProjectSnapshot): Blob {
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const ppq = snapshot.ppq ?? 480 // Use original ppq if available, otherwise default to 480
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const microsecondsPerBeat = Math.round(60000000 / snapshot.tempo) // Convert BPM to microseconds per beat
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// Sort notes by start time, then by midi for stable ordering
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const sortedNotes = [...snapshot.notes].sort((a, b) => a.start - b.start || a.midi - b.midi)
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// Build events for a single track containing both lyrics and notes
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// Event order at same tick: note_off (0) < lyrics (1) < note_on (2)
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// This matches meta.py's tg2midi implementation
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const events: Array<WithAbsoluteTime<MidiEvent>> = []
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// Add all note events and their corresponding lyrics
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sortedNotes.forEach((note) => {
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const startTicks = Math.round(note.start * ppq)
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const endTicks = Math.round((note.start + note.duration) * ppq)
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const velocity = Math.round(note.velocity * 127)
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// Add lyric event at the same tick as note_on (but will be sorted before it)
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const lyricText = note.lyric ?? ''
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const encodedLyric = encodeUtf8ByteString(lyricText)
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// Lyric event - sort key 1 (after note_off, before note_on)
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events.push({
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absoluteTime: startTicks,
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deltaTime: 0,
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meta: true,
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type: 'lyrics',
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text: encodedLyric,
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_sortKey: 1,
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} as WithAbsoluteTime<MidiEvent> & { _sortKey: number })
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// Note on event - sort key 2 (after lyrics)
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events.push({
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absoluteTime: startTicks,
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deltaTime: 0,
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type: 'noteOn',
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channel: 0,
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noteNumber: note.midi,
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velocity: velocity,
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_sortKey: 2,
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} as WithAbsoluteTime<MidiEvent> & { _sortKey: number })
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// Note off event - sort key 0 (before everything at same tick)
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events.push({
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absoluteTime: endTicks,
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deltaTime: 0,
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type: 'noteOff',
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channel: 0,
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noteNumber: note.midi,
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velocity: 0,
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_sortKey: 0,
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} as WithAbsoluteTime<MidiEvent> & { _sortKey: number })
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})
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// Sort events by absoluteTime, then by _sortKey
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events.sort((a, b) => {
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const aKey = (a as { _sortKey?: number })._sortKey ?? 1
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const bKey = (b as { _sortKey?: number })._sortKey ?? 1
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return a.absoluteTime - b.absoluteTime || aKey - bKey
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})
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// Convert absolute time to delta time
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let lastTick = 0
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events.forEach(event => {
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event.deltaTime = event.absoluteTime - lastTick
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lastTick = event.absoluteTime
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delete (event as { absoluteTime?: number }).absoluteTime
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delete (event as { _sortKey?: number })._sortKey
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})
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// Build the MIDI track with header events
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const track: MidiEvent[] = [
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// Set tempo
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{
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deltaTime: 0,
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meta: true,
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type: 'setTempo',
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microsecondsPerBeat: microsecondsPerBeat,
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},
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// Time signature
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{
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deltaTime: 0,
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meta: true,
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type: 'timeSignature',
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numerator: snapshot.timeSignature[0],
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denominator: snapshot.timeSignature[1],
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metronome: 24,
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thirtyseconds: 8,
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},
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// All note and lyric events
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...events,
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// End of track
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{
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deltaTime: 0,
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meta: true,
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type: 'endOfTrack',
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},
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]
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// Build MIDI data structure
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const midiData: MidiData = {
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header: {
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format: 0, // Single track format (type 0)
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numTracks: 1,
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ticksPerBeat: ppq,
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},
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tracks: [track],
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}
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const bytes = writeMidi(midiData)
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return new Blob([new Uint8Array(bytes)], { type: 'audio/midi' })
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}
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