diff --git a/.gitignore b/.gitignore
index f7da770..4d60acc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,6 +18,10 @@ Thumbs.db
 !.env.example
 !.env.test
 
+# Test temp files
+tmp-test-remux/
+tmp-test-*/
+
 # Vite
 vite.config.js.timestamp-*
 vite.config.ts.timestamp-*
diff --git a/src/tests/fixtures/medarecorder-emu.webm b/src/tests/fixtures/medarecorder-emu.webm
index 336d911..edf8d5c 100644
Binary files a/src/tests/fixtures/medarecorder-emu.webm and b/src/tests/fixtures/medarecorder-emu.webm differ
diff --git a/src/tests/remux.integration.test.ts b/src/tests/remux.integration.test.ts
index 23ff776..78e6288 100644
--- a/src/tests/remux.integration.test.ts
+++ b/src/tests/remux.integration.test.ts
@@ -6,12 +6,13 @@ import { execFileSync } from 'child_process';
 /**
  * Integration test for webm remux using real ffmpeg.
  *
- * FIXTURE NOTE: The fixture (fixtures/medarecorder-emu.webm) is generated
- * by ffmpeg from a silent audio source, NOT captured from a real PWA
- * MediaRecorder session. It may NOT reproduce the exact no-Cues /
- * unset-duration characteristics of real browser output.
- * This test is flagged LOWER-CONFIDENCE for the MediaRecorder regression
- * aspect per the story specification.
+ * FIXTURE NOTE: The fixture (fixtures/medarecorder-emu.webm) is generated by
+ * ffmpeg -live 1 from a silent audio source (NOT a real PWA MediaRecorder
+ * capture). The -live 1 flag suppresses Cues and Duration in the Segment
+ * Info header, producing a file that emulates the "no Cues, unset/streaming
+ * duration" characteristic of browser MediaRecorder opus-in-webm output.
+ * This synthetic fixture is LOWER-CONFIDENCE than a real PWA capture but
+ * DOES reproduce the specific ffprobe Duration=N/A failure mode.
  */
 describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 	const fixturePath = join(__dirname, 'fixtures', 'medarecorder-emu.webm');
@@ -21,7 +22,7 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 		if (!existsSync(fixturePath)) {
 			throw new Error(
 				`Fixture not found at ${fixturePath}. Generate with:\n` +
-				`  ffmpeg -f lavfi -i anullsrc=r=48000:cl=mono -t 2 -c:a libopus -b:a 32k -f webm ${fixturePath}`
+				`  ffmpeg -f lavfi -i anullsrc=r=48000:cl=mono -t 2 -c:a libopus -b:a 32k -f webm -live 1 ${fixturePath}`
 			);
 		}
 		if (!existsSync(tmpDir)) {
@@ -30,10 +31,27 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 	});
 
 	afterAll(() => {
-		// Clean up temp dir
 		try { unlinkSync(join(tmpDir, 'integration-test.webm')); } catch {}
 		try { unlinkSync(join(tmpDir, 'integration-test.webm.out')); } catch {}
 		try { unlinkSync(join(tmpDir, 'integration-test.webm.remuxed')); } catch {}
+		try { unlinkSync(join(tmpDir, 'fixture-test-remuxed.webm')); } catch {}
+		try { unlinkSync(join(tmpDir, 'integration-audio-chain.webm')); } catch {}
+		try { unlinkSync(join(tmpDir, 'integration-audio-chain.wav')); } catch {}
+	});
+
+	it('fixture input lacks duration (emulates MediaRecorder streaming output)', () => {
+		const probeIn = execFileSync('ffprobe', [
+			'-v', 'quiet',
+			'-print_format', 'json',
+			'-show_format',
+			fixturePath
+		], { encoding: 'utf8' });
+
+		const info = JSON.parse(probeIn);
+
+		// Fixture generated with -live 1: no Duration in Segment Info
+		expect(info.format.duration).toBeUndefined();
+		expect(info.format.format_name).toMatch(/matroska|webm/i);
 	});
 
 	it('remux produces a valid webm with finalized duration', () => {
@@ -41,7 +59,7 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 		const outFile = join(tmpDir, 'integration-test.webm.remuxed');
 		copyFileSync(fixturePath, testFile);
 
-		// Run ffmpeg remux — same command as remuxUpload()
+		// remux via ffmpeg (same args as remuxUpload)
 		execFileSync('ffmpeg', [
 			'-y',
 			'-i', testFile,
@@ -51,12 +69,12 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 			outFile
 		]);
 
-		// Output exists and non-empty
+		// output file exists and non-empty
 		expect(existsSync(outFile)).toBe(true);
 		const outSize = readFileSync(outFile).length;
 		expect(outSize).toBeGreaterThan(0);
 
-		// Verify with ffprobe
+		// probe output streams and duration
 		const probeOut = execFileSync('ffprobe', [
 			'-v', 'quiet',
 			'-print_format', 'json',
@@ -70,12 +88,12 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 		expect(info.streams[0].codec_name).toBe('opus');
 		expect(info.format.format_name).toMatch(/matroska|webm/i);
 
-		// Duration should be present after remux
+		// duration is now finalized
 		const duration = parseFloat(info.format.duration);
 		expect(duration).toBeGreaterThan(0);
-		expect(duration).toBeCloseTo(2.0, 0); // ~2s as generated
+		expect(duration).toBeCloseTo(2.0, 0); // approx 2s source
 
-		// Remux is idempotent: re-run on output produces same duration
+		// idempotent: second remux pass preserves duration
 		const outFile2 = join(tmpDir, 'integration-test.webm.remuxed2');
 		execFileSync('ffmpeg', [
 			'-y',
@@ -94,14 +112,92 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 		const info2 = JSON.parse(probeOut2);
 		expect(parseFloat(info2.format.duration)).toBeCloseTo(2.0, 0);
 
-		// Cleanup
+		// cleanup
 		unlinkSync(outFile);
 		unlinkSync(outFile2);
 		unlinkSync(testFile);
 	});
 
+	it('remuxUpload function accepts fixture and fixes duration', async () => {
+		const testFile = join(tmpDir, 'fixture-test-remuxed.webm');
+		copyFileSync(fixturePath, testFile);
+
+		// confirm input has no duration before remux
+		const beforeProbe = execFileSync('ffprobe', [
+			'-v', 'quiet',
+			'-print_format', 'json',
+			'-show_format',
+			testFile
+		], { encoding: 'utf8' });
+		expect(JSON.parse(beforeProbe).format.duration).toBeUndefined();
+
+		// call the actual module function via dynamic import
+		const { remuxUpload } = await import('$lib/server/remux.js');
+		const result = await remuxUpload(testFile, 'fixture-test');
+
+		expect(result).toBe(testFile);
+
+		// after remux: duration is finalized
+		const afterProbe = execFileSync('ffprobe', [
+			'-v', 'quiet',
+			'-print_format', 'json',
+			'-show_format',
+			testFile
+		], { encoding: 'utf8' });
+		const afterInfo = JSON.parse(afterProbe);
+		const duration = parseFloat(afterInfo.format.duration);
+		expect(duration).toBeGreaterThan(0);
+		expect(duration).toBeCloseTo(2.0, 0);
+
+		unlinkSync(testFile);
+	});
+
+	it('remuxed output is consumable by prepareAudio-equivalent ffmpeg convert', () => {
+		const testFile = join(tmpDir, 'integration-audio-chain.webm');
+		const wavFile = join(tmpDir, 'integration-audio-chain.wav');
+		copyFileSync(fixturePath, testFile);
+
+		// remux in-place (same as pipeline does)
+		execFileSync('ffmpeg', [
+			'-y',
+			'-i', testFile,
+			'-c', 'copy',
+			'-fflags', '+genpts',
+			'-f', 'webm',
+			testFile + '.fixed'
+		]);
+		copyFileSync(testFile + '.fixed', testFile);
+		unlinkSync(testFile + '.fixed');
+
+		// prepareAudio's core: ffmpeg -> 16kHz mono WAV
+		execFileSync('ffmpeg', [
+			'-y',
+			'-i', testFile,
+			'-ar', '16000', '-ac', '1',
+			'-c:a', 'pcm_s16le',
+			wavFile
+		]);
+
+		expect(existsSync(wavFile)).toBe(true);
+		const wavStat = readFileSync(wavFile);
+		expect(wavStat.length).toBeGreaterThan(1000);
+
+		const probe = execFileSync('ffprobe', [
+			'-v', 'quiet',
+			'-print_format', 'json',
+			'-show_format',
+			wavFile
+		], { encoding: 'utf8' });
+		const info = JSON.parse(probe);
+		expect(info.format.format_name).toMatch(/wav/i);
+		expect(parseFloat(info.format.duration)).toBeGreaterThan(0);
+
+		unlinkSync(testFile);
+		unlinkSync(wavFile);
+	});
+
 	it('non-webm files are unaffected by remux command', () => {
-		// Generate a minimal valid mp4 with ffmpeg
+		// generate a non-webm-like file using webm container
 		const testFile = join(tmpDir, 'test-non.webm');
 		execFileSync('ffmpeg', [
 			'-y',
@@ -112,10 +208,7 @@ describe('remux — integration (lower-confidence: synthetic fixture)', () => {
 			testFile
 		]);
 
-		// Rename to .mp4 (wrong extension, but same format)
-		const mp4File = testFile + '.mp4';
-		// Actually just use original extension - this test proves non-webm pass-through
-		// by running the same ffmpeg command on it
+		// remux command doesn't choke on it
 		const outFile = join(tmpDir, 'test-non-out.webm');
 		execFileSync('ffmpeg', [
 			'-y',