diff --git a/src/__tests__/midi-writer.test.ts b/src/__tests__/midi-writer.test.ts
new file mode 100644
index 0000000..c8d3af1
--- /dev/null
+++ b/src/__tests__/midi-writer.test.ts
@@ -0,0 +1,131 @@
+/**
+ * Round-trip tests for writeMidiFile.
+ *
+ * All tests exercise the writer only through parseChartAndIni: build a
+ * ParsedChart, write it out as MIDI, re-parse, and assert on the resulting
+ * ParsedChart. No assertions about the raw MIDI structure (track count,
+ * track names, note numbers, setTempo microseconds, text-event brackets,
+ * etc.) — the parser is the source of truth for observable behavior.
+ */
+
+import type { MidiEvent } from '@geomitron/midi-file'
+import { describe, expect, it } from 'vitest'
+
+import { createEmptyChart } from '../chart/create-chart'
+import { writeMidiFile } from '../chart/midi-writer'
+import { parseChartAndIni, type ParsedChart } from '../chart/parse-chart-and-ini'
+
+function roundTrip(chart: ParsedChart, iniText?: string): ParsedChart {
+	const files: { fileName: string; data: Uint8Array }[] = [
+		{ fileName: 'notes.mid', data: writeMidiFile(chart) },
+	]
+	if (iniText !== undefined) {
+		files.push({ fileName: 'song.ini', data: new TextEncoder().encode(iniText) })
+	}
+	const result = parseChartAndIni(files)
+	if (!result.parsedChart) {
+		throw new Error(`round-trip produced no parsedChart: ${JSON.stringify(result.chartFolderIssues)}`)
+	}
+	return result.parsedChart
+}
+
+describe('writeMidiFile round-trip: resolution + [SyncTrack]', () => {
+	it('preserves chart resolution', () => {
+		const re = roundTrip(createEmptyChart({ resolution: 192 }))
+		expect(re.resolution).toBe(192)
+	})
+
+	it('preserves the default tempo on an empty chart', () => {
+		const re = roundTrip(createEmptyChart({ bpm: 120 }))
+		expect(re.tempos.map(t => ({ tick: t.tick, bpm: Math.round(t.beatsPerMinute) }))).toEqual([{ tick: 0, bpm: 120 }])
+	})
+
+	it('preserves fractional BPM within microsecondsPerBeat rounding', () => {
+		const re = roundTrip(createEmptyChart({ bpm: 137.5 }))
+		// setTempo is stored as integer microseconds/beat, so fractional BPM
+		// round-trips with tiny quantization — check within 0.01 BPM.
+		expect(re.tempos[0].beatsPerMinute).toBeCloseTo(137.5, 1)
+	})
+
+	it('preserves multiple tempo changes at their ticks', () => {
+		const chart = createEmptyChart({ resolution: 480, bpm: 120 })
+		chart.tempos.push({ tick: 960, beatsPerMinute: 180, msTime: 0 })
+		const re = roundTrip(chart)
+		expect(re.tempos.map(t => ({ tick: t.tick, bpm: Math.round(t.beatsPerMinute) }))).toEqual([
+			{ tick: 0, bpm: 120 },
+			{ tick: 960, bpm: 180 },
+		])
+	})
+
+	it('preserves non-4/4 time signatures', () => {
+		const chart = createEmptyChart({ timeSignature: { numerator: 6, denominator: 8 } })
+		expect(roundTrip(chart).timeSignatures[0]).toMatchObject({ numerator: 6, denominator: 8 })
+	})
+
+	it('preserves multiple time-signature changes', () => {
+		const chart = createEmptyChart({ timeSignature: { numerator: 7, denominator: 8 } })
+		chart.timeSignatures.push({ tick: 3840, numerator: 3, denominator: 4, msTime: 0, msLength: 0 })
+		const re = roundTrip(chart)
+		expect(re.timeSignatures.map(ts => ({ t: ts.tick, n: ts.numerator, d: ts.denominator }))).toEqual([
+			{ t: 0, n: 7, d: 8 },
+			{ t: 3840, n: 3, d: 4 },
+		])
+	})
+})
+
+describe('writeMidiFile round-trip: EVENTS track', () => {
+	it('preserves sections at the right ticks with correct names', () => {
+		const chart = createEmptyChart()
+		chart.sections.push({ tick: 0, name: 'Intro', msTime: 0, msLength: 0 })
+		chart.sections.push({ tick: 1920, name: 'Verse 1', msTime: 0, msLength: 0 })
+		const re = roundTrip(chart)
+		expect(re.sections.map(s => ({ tick: s.tick, name: s.name }))).toEqual([
+			{ tick: 0, name: 'Intro' },
+			{ tick: 1920, name: 'Verse 1' },
+		])
+	})
+
+	it('preserves end events', () => {
+		const chart = createEmptyChart()
+		chart.endEvents.push({ tick: 1920, msTime: 0, msLength: 0 })
+		expect(roundTrip(chart).endEvents.map(e => e.tick)).toEqual([1920])
+	})
+
+	it('preserves unrecognized EVENTS events on .mid source', () => {
+		const chart = createEmptyChart({ format: 'mid' })
+		chart.unrecognizedEventsTrackTextEvents.push({ tick: 480, text: 'crowd_noclap', msTime: 0, msLength: 0 })
+		const re = roundTrip(chart)
+		expect(re.unrecognizedEventsTrackTextEvents.map(e => ({ tick: e.tick, text: e.text }))).toEqual([
+			{ tick: 480, text: 'crowd_noclap' },
+		])
+	})
+})
+
+describe('writeMidiFile round-trip: unrecognized MIDI tracks', () => {
+	it('preserves an unrecognized track by name', () => {
+		const chart = createEmptyChart()
+		chart.unrecognizedMidiTracks.push({
+			trackName: 'CUSTOM',
+			events: [
+				{ deltaTime: 0, meta: true, type: 'trackName', text: 'CUSTOM' } as MidiEvent,
+				{ deltaTime: 240, meta: true, type: 'text', text: 'hello' } as MidiEvent,
+				{ deltaTime: 240, meta: true, type: 'endOfTrack' } as MidiEvent,
+			],
+		})
+		expect(roundTrip(chart).unrecognizedMidiTracks.map(t => t.trackName)).toEqual(['CUSTOM'])
+	})
+
+	it('preserves multiple unrecognized tracks with the same name', () => {
+		const chart = createEmptyChart()
+		for (let i = 0; i < 3; i++) {
+			chart.unrecognizedMidiTracks.push({
+				trackName: 'CUSTOM',
+				events: [
+					{ deltaTime: 0, meta: true, type: 'trackName', text: 'CUSTOM' } as MidiEvent,
+					{ deltaTime: 0, meta: true, type: 'endOfTrack' } as MidiEvent,
+				],
+			})
+		}
+		expect(roundTrip(chart).unrecognizedMidiTracks).toHaveLength(3)
+	})
+})
diff --git a/src/chart/index.ts b/src/chart/index.ts
index 4661673..f7761fe 100644
--- a/src/chart/index.ts
+++ b/src/chart/index.ts
@@ -1,4 +1,5 @@
 export * from './chart-scanner'
 export * from './chart-writer'
 export * from './create-chart'
+export * from './midi-writer'
 export * from './parse-chart-and-ini'
diff --git a/src/chart/midi-writer.ts b/src/chart/midi-writer.ts
new file mode 100644
index 0000000..265f599
--- /dev/null
+++ b/src/chart/midi-writer.ts
@@ -0,0 +1,259 @@
+/**
+ * MIDI binary writer — serializes a ParsedChart back to a Format-1 `.mid` file.
+ *
+ * This PR establishes the writer infrastructure:
+ *   - `writeMidiFile` entry point
+ *   - TEMPO TRACK (tempo + time-signature meta events)
+ *   - EVENTS track (sections + end events + unrecognized global events + coda)
+ *   - Unrecognized MIDI tracks (verbatim pass-through)
+ *   - `finalizeMidiTrack` shared helper (sort + absolute→delta time conversion)
+ *
+ * Instrument tracks (PART DRUMS, PART GUITAR, etc.) and vocal tracks
+ * (PART VOCALS, HARM1/2/3) are emitted by follow-up PRs.
+ */
+
+import type { MidiData, MidiEvent } from '@geomitron/midi-file'
+import { writeMidi } from '@geomitron/midi-file'
+
+import type { ParsedChart } from './parse-chart-and-ini'
+
+// ---------------------------------------------------------------------------
+// Internal types
+// ---------------------------------------------------------------------------
+
+/** A MIDI event tagged with its absolute tick (for sort-then-delta finalization). */
+export interface AbsoluteEvent {
+	tick: number
+	event: MidiEvent
+	/** Stable sort tiebreaker — preserves source ordering within the same tick. */
+	seq?: number
+}
+
+// ---------------------------------------------------------------------------
+// Public API
+// ---------------------------------------------------------------------------
+
+/**
+ * Serialize a {@link ParsedChart} to `.mid` bytes.
+ *
+ * Output track layout:
+ *   0 — TEMPO TRACK (BPM + time signatures)
+ *   1 — EVENTS (sections, end events, global events, coda)
+ *   N — Unrecognized MIDI tracks (verbatim pass-through)
+ *
+ * Instrument tracks (PART DRUMS, PART GUITAR, …) and vocal tracks
+ * (PART VOCALS, HARM1/2/3) are emitted by follow-up PRs — this entry point
+ * currently skips `chart.trackData` and `chart.vocalTracks`.
+ */
+export function writeMidiFile(chart: ParsedChart): Uint8Array {
+	const trackMap = new Map<string, MidiEvent[]>()
+
+	trackMap.set('TEMPO TRACK', buildTempoTrack(chart))
+	trackMap.set('EVENTS', buildEventsTrack(chart))
+
+	// Unrecognized whole tracks (VENUE, BEAT, PART REAL_*, custom tracks) are
+	// round-tripped verbatim.
+	let dupSuffix = 0
+	for (const ut of chart.unrecognizedMidiTracks) {
+		let mapKey = ut.trackName
+		while (trackMap.has(mapKey)) mapKey = `${ut.trackName}__dup${dupSuffix++}`
+		trackMap.set(mapKey, buildUnrecognizedTrack(ut.events))
+	}
+
+	const tracks = [...trackMap.values()]
+	const midiData: MidiData = {
+		header: {
+			format: 1,
+			numTracks: tracks.length,
+			ticksPerBeat: chart.resolution,
+		},
+		tracks,
+	}
+	return new Uint8Array(writeMidi(midiData))
+}
+
+// ---------------------------------------------------------------------------
+// Track builders
+// ---------------------------------------------------------------------------
+
+function buildTempoTrack(chart: ParsedChart): MidiEvent[] {
+	const events: AbsoluteEvent[] = []
+
+	events.push({
+		tick: 0,
+		event: { deltaTime: 0, meta: true, type: 'trackName', text: 'TEMPO TRACK' } as MidiEvent,
+	})
+
+	for (const tempo of chart.tempos) {
+		events.push({
+			tick: tempo.tick,
+			event: {
+				deltaTime: 0,
+				meta: true,
+				type: 'setTempo',
+				microsecondsPerBeat: Math.round(60_000_000 / tempo.beatsPerMinute),
+			} as MidiEvent,
+		})
+	}
+
+	for (const ts of chart.timeSignatures) {
+		events.push({
+			tick: ts.tick,
+			event: {
+				deltaTime: 0,
+				meta: true,
+				type: 'timeSignature',
+				numerator: ts.numerator,
+				denominator: ts.denominator,
+				metronome: 24,
+				thirtyseconds: 8,
+			} as MidiEvent,
+		})
+	}
+
+	return finalizeMidiTrack(events)
+}
+
+function buildEventsTrack(chart: ParsedChart): MidiEvent[] {
+	const events: AbsoluteEvent[] = []
+
+	events.push({
+		tick: 0,
+		event: { deltaTime: 0, meta: true, type: 'trackName', text: 'EVENTS' } as MidiEvent,
+	})
+
+	// Sections emit UNWRAPPED as `section name` (not `[section name]`). YARG's
+	// NormalizeTextEvent strips content between the first `[` and first `]`,
+	// which would lose data for names that contain `]`. Unwrapped form preserves
+	// names with `]` and names starting with `[`. The only case that's inherently
+	// lossy under YARG normalization is names containing both `[` and `]` —
+	// those can't round-trip regardless of wrapping.
+	for (const section of chart.sections) {
+		events.push({
+			tick: section.tick,
+			event: { deltaTime: 0, meta: true, type: 'text', text: `section ${section.name}` } as MidiEvent,
+		})
+	}
+
+	for (const endEvent of chart.endEvents) {
+		events.push({
+			tick: endEvent.tick,
+			event: { deltaTime: 0, meta: true, type: 'text', text: '[end]' } as MidiEvent,
+		})
+	}
+
+	// Global events (crowd events, music_start/end, coda, etc.). `.chart`
+	// stores them unwrapped; `.mid` stores them bracket-wrapped. When the
+	// source was `.chart`, wrap on output so the MIDI output follows convention.
+	const sourceIsMidi = chart.format === 'mid'
+	for (const ge of chart.unrecognizedEventsTrackTextEvents) {
+		let text = ge.text
+		if (!sourceIsMidi) {
+			const trimmed = text.trimEnd()
+			if (!(trimmed.startsWith('[') && trimmed.endsWith(']'))) {
+				text = `[${text}]`
+			}
+		}
+		events.push({
+			tick: ge.tick,
+			event: { deltaTime: 0, meta: true, type: 'text', text } as MidiEvent,
+		})
+	}
+
+	// Coda events: derive from drumFreestyleSections only if none already in
+	// unrecognizedEventsTrackTextEvents. The parser splits [coda] into both
+	// places, but we only need one.
+	const hasCodaInGlobalEvents = chart.unrecognizedEventsTrackTextEvents.some(ge => {
+		const trimmed = ge.text.trim()
+		return trimmed === '[coda]' || trimmed === 'coda'
+	})
+	if (!hasCodaInGlobalEvents) {
+		const codaTicks = new Set<number>()
+		for (const track of chart.trackData) {
+			for (const fs of track.drumFreestyleSections) {
+				if (fs.isCoda) codaTicks.add(fs.tick)
+			}
+		}
+		for (const tick of codaTicks) {
+			events.push({
+				tick,
+				event: { deltaTime: 0, meta: true, type: 'text', text: '[coda]' } as MidiEvent,
+			})
+		}
+	}
+
+	return finalizeMidiTrack(events)
+}
+
+/**
+ * Re-emit a parsed unrecognized track verbatim.
+ *
+ * Events arrive with `deltaTime = absolute tick` (scan-chart's
+ * `convertToAbsoluteTime` post-processing). midi-file's writer expects delta
+ * timing, so convert back here.
+ *
+ * If the input MIDI was malformed (non-monotonic absolute ticks → negative
+ * deltas), midi-file's writeVarInt will throw. We let that bubble up so the
+ * caller can record it as a per-chart failure rather than silently reorder
+ * events to "fix" the malformed source.
+ */
+function buildUnrecognizedTrack(events: MidiEvent[]): MidiEvent[] {
+	let prevTick = 0
+	const out: MidiEvent[] = []
+	for (const e of events) {
+		const absTick = e.deltaTime
+		out.push({ ...e, deltaTime: absTick - prevTick })
+		prevTick = absTick
+	}
+	return out
+}
+
+// ---------------------------------------------------------------------------
+// Shared helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * Sort events by absolute tick (with a type-priority tiebreaker) and convert
+ * to delta-time encoding. Appends an `endOfTrack` meta event.
+ *
+ * Sort priority at the same tick: trackName → timeSignature → setTempo →
+ * noteOff → sysEx → noteOn → text/lyrics → other → endOfTrack. This matches
+ * Clone Hero's expected event ordering. Events with an explicit `seq` tag
+ * sort AFTER untagged events at the same tick (so instrument-track emitters
+ * can sequence paired events deterministically via `seq`).
+ */
+export function finalizeMidiTrack(events: AbsoluteEvent[]): MidiEvent[] {
+	const eventPriority = (e: MidiEvent): number => {
+		switch (e.type) {
+			case 'trackName': return 0
+			case 'timeSignature': return 1
+			case 'setTempo': return 2
+			case 'noteOff': return 3
+			case 'sysEx': case 'endSysEx': return 4
+			case 'noteOn': return 5
+			case 'text': case 'lyrics': return 6
+			case 'endOfTrack': return 8
+			default: return 7
+		}
+	}
+	events.sort((a, b) => {
+		if (a.tick !== b.tick) return a.tick - b.tick
+		const aHasSeq = a.seq !== undefined
+		const bHasSeq = b.seq !== undefined
+		if (!aHasSeq && !bHasSeq) return eventPriority(a.event) - eventPriority(b.event)
+		if (!aHasSeq) return -1
+		if (!bHasSeq) return 1
+		return (a.seq as number) - (b.seq as number)
+	})
+
+	let prevTick = 0
+	const midiEvents: MidiEvent[] = []
+	for (const { tick, event } of events) {
+		event.deltaTime = tick - prevTick
+		prevTick = tick
+		midiEvents.push(event)
+	}
+
+	midiEvents.push({ deltaTime: 0, meta: true, type: 'endOfTrack' } as MidiEvent)
+	return midiEvents
+}