From 78e78e5b4f3ff92603a01c540d7b7a9bbb694e65 Mon Sep 17 00:00:00 2001
From: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
Date: Mon, 12 Jan 2026 14:36:51 +0100
Subject: [PATCH] Make _flushOrWaitForOngoingClose set closingPromise (fixes
 #270)

---
 src/media-source.ts                | 10 ++++-----
 test/browser/media-sources.test.ts | 35 ++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 6 deletions(-)
 create mode 100644 test/browser/media-sources.test.ts

diff --git a/src/media-source.ts b/src/media-source.ts
index 7b5cae6..ddf746b 100644
--- a/src/media-source.ts
+++ b/src/media-source.ts
@@ -134,12 +134,10 @@ export abstract class MediaSource {
 
 	/** @internal */
 	async _flushOrWaitForOngoingClose(forceClose: boolean) {
-		if (this._closingPromise) {
-			// Since closing also flushes, we don't want to do it twice
-			return this._closingPromise;
-		} else {
-			return this._flushAndClose(forceClose);
-		}
+		return this._closingPromise ??= (async () => {
+			await this._flushAndClose(forceClose);
+			this._closed = true;
+		})();
 	}
 }
 
diff --git a/test/browser/media-sources.test.ts b/test/browser/media-sources.test.ts
new file mode 100644
index 0000000..cd218ba
--- /dev/null
+++ b/test/browser/media-sources.test.ts
@@ -0,0 +1,35 @@
+import { test } from 'vitest';
+import { Output } from '../../src/output.js';
+import { WebMOutputFormat } from '../../src/output-format.js';
+import { BufferTarget } from '../../src/target.js';
+import { VideoSampleSource } from '../../src/media-source.js';
+import { VideoSample } from '../../src/sample.js';
+import { QUALITY_MEDIUM } from '../../src/encode.js';
+
+test('VideoSampleSource.close() should be idempotent after finalize()', async () => {
+	const output = new Output({
+		format: new WebMOutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const videoSource = new VideoSampleSource({
+		codec: 'vp8',
+		bitrate: QUALITY_MEDIUM,
+	});
+
+	output.addVideoTrack(videoSource);
+	await output.start();
+
+	const canvas = new OffscreenCanvas(100, 100);
+	const ctx = canvas.getContext('2d')!;
+	ctx.fillStyle = 'red';
+	ctx.fillRect(0, 0, 100, 100);
+
+	const sample = new VideoSample(canvas, { timestamp: 0, duration: 1 / 30 });
+	await videoSource.add(sample);
+	sample.close();
+
+	await output.finalize();
+
+	videoSource.close(); // This previously threw
+});