diff --git a/src/viewport/VideoLibrary.ts b/src/viewport/VideoLibrary.ts
index 1bd6305f..bed248a4 100644
--- a/src/viewport/VideoLibrary.ts
+++ b/src/viewport/VideoLibrary.ts
@@ -36,6 +36,15 @@ export class VideoLibrary {
   private heard = false;
   private paused = false;
   private sweeper: ReturnType<typeof setInterval> | null = null;
+  /** When the page was last shown, by `performance.now()`; see `sweep`. */
+  private shown = 0;
+
+  constructor() {
+    if (typeof document === 'undefined') return;
+    document.addEventListener('visibilitychange', () => {
+      if (!document.hidden) this.shown = performance.now();
+    });
+  }
 
   /** Runs `fn` whenever a player has its first picture; returns the unsubscribe. */
   onChange(fn: () => void): () => void {
@@ -85,12 +94,16 @@ export class VideoLibrary {
     this.stopSweeping();
   }
 
-  /** Drops the players nobody asked for lately; a paused run asks for nothing and keeps them. */
+  /**
+   * Drops the players nobody asked for lately; a paused run asks for nothing and keeps them. So
+   * does a hidden page: Chrome draws no frames for it while its timers go on, and a sprite that
+   * still wears a video would lose it. The time hidden does not count as idle.
+   */
   private sweep(): void {
-    if (this.paused) return;
+    if (this.paused || document.hidden) return;
     const now = performance.now();
     for (const [key, player] of this.players)
-      if (now - player.asked > IDLE_MS) {
+      if (now - Math.max(player.asked, this.shown) > IDLE_MS) {
         this.drop(player);
         this.players.delete(key);
       }
@@ -181,12 +194,14 @@ export class VideoLibrary {
     player.element.load();
     // The texture itself stays whole: a wearer that has not synced since still draws it, and a
     // destroyed one has no source and threw in the batcher. It shows nothing until the wearer asks
-    // again; only the video behind it is let go.
+    // again. The video source is only unloaded, not destroyed: a shader may still hold it until
+    // its wearer syncs, and Pixi warns about every destroyed source still bound to one.
     const texture = player.texture;
     if (!texture) return;
-    const video = texture.source;
+    const video = texture.source as VideoSource;
     texture.source = Texture.EMPTY.source;
-    video.destroy();
+    video.autoUpdate = false;
+    video.unload();
   }
 
   private notify(): void {
diff --git a/tests/viewport/video-library.test.ts b/tests/viewport/video-library.test.ts
new file mode 100644
index 00000000..3eb3cb89
--- /dev/null
+++ b/tests/viewport/video-library.test.ts
@@ -0,0 +1,86 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+/**
+ * When the video library lets a player go (#402): after 2 s nobody asked for it, but never while
+ * the page is hidden. Chrome draws no frames for a hidden page and so nothing asks, while the
+ * sweeper's timer goes on; a sprite still wearing the video lost it and Pixi warned about the
+ * destroyed source on the way back.
+ */
+const KEY = `video:a1b2c3d4e5f6/${'c7'.repeat(32)}.mp4#0~0~1~1`;
+
+function fakeVideo() {
+  return {
+    muted: false,
+    playsInline: false,
+    preload: '',
+    src: '',
+    currentTime: 0,
+    loop: false,
+    paused: true,
+    addEventListener: () => {},
+    requestVideoFrameCallback: () => 0,
+    play: () => Promise.resolve(),
+    pause: () => {},
+    removeAttribute: () => {},
+    load: () => {},
+  };
+}
+
+const page = { hidden: false, listeners: [] as (() => void)[] };
+
+function setHidden(hidden: boolean): void {
+  page.hidden = hidden;
+  for (const listener of page.listeners) listener();
+}
+
+async function freshLibrary() {
+  const { VideoLibrary } = await import('../../src/viewport/VideoLibrary');
+  return new VideoLibrary();
+}
+
+describe('VideoLibrary sweeping', () => {
+  beforeEach(() => {
+    vi.useFakeTimers({ toFake: ['setInterval', 'clearInterval', 'performance'] });
+    page.hidden = false;
+    page.listeners = [];
+    vi.stubGlobal('document', {
+      get hidden() {
+        return page.hidden;
+      },
+      addEventListener: (_type: string, listener: () => void) => page.listeners.push(listener),
+      createElement: fakeVideo,
+    });
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    vi.unstubAllGlobals();
+  });
+
+  it('lets a player go that nobody asked for in 2 s', async () => {
+    const videos = await freshLibrary();
+    videos.get(KEY);
+    vi.advanceTimersByTime(4100);
+    expect(videos.debugInfo()).toEqual([]);
+  });
+
+  it('keeps it while the page is hidden, however long', async () => {
+    const videos = await freshLibrary();
+    videos.get(KEY);
+    setHidden(true);
+    vi.advanceTimersByTime(60_000);
+    expect(videos.debugInfo()).toHaveLength(1);
+  });
+
+  it('does not count the time hidden as idle once the page is back', async () => {
+    const videos = await freshLibrary();
+    videos.get(KEY);
+    setHidden(true);
+    vi.advanceTimersByTime(60_000);
+    setHidden(false);
+    vi.advanceTimersByTime(1900);
+    expect(videos.debugInfo()).toHaveLength(1);
+    vi.advanceTimersByTime(2200);
+    expect(videos.debugInfo()).toEqual([]);
+  });
+});
diff --git a/tools/ci/router.php b/tools/ci/router.php
new file mode 100644
index 00000000..6238181f
--- /dev/null
+++ b/tools/ci/router.php
@@ -0,0 +1,45 @@
+<?php
+// Router of the CI jobs' dev server (see serve.sh). `php -S` answers no Range requests, and Chrome
+// cannot seek in a video served without them (#402): a clip stayed at the video's first frame. On
+// stein2 nginx does this. Here the converted videos get their ranges; everything else is left to
+// the server as before.
+
+$path = rawurldecode((string) parse_url($_SERVER['REQUEST_URI'] ?? '', PHP_URL_PATH));
+if (!preg_match('#^/game-maker/data/videos/[0-9a-z]+/[0-9a-f]{64}\.mp4$#', $path)) {
+    return false;
+}
+$file = $_SERVER['DOCUMENT_ROOT'] . $path;
+if (!is_file($file)) {
+    return false;
+}
+
+$size = filesize($file);
+$start = 0;
+$end = $size - 1;
+header('Content-Type: video/mp4');
+header('Accept-Ranges: bytes');
+if (preg_match('/^bytes=(\d*)-(\d*)$/', $_SERVER['HTTP_RANGE'] ?? '', $range)) {
+    if ($range[1] === '') {
+        $start = max(0, $size - (int) $range[2]);
+    } else {
+        $start = (int) $range[1];
+        if ($range[2] !== '') {
+            $end = min($end, (int) $range[2]);
+        }
+    }
+    if ($start > $end) {
+        http_response_code(416);
+        header("Content-Range: bytes */$size");
+        return true;
+    }
+    http_response_code(206);
+    header("Content-Range: bytes $start-$end/$size");
+}
+header('Content-Length: ' . ($end - $start + 1));
+if ($_SERVER['REQUEST_METHOD'] === 'HEAD') {
+    return true;
+}
+$in = fopen($file, 'rb');
+$out = fopen('php://output', 'wb');
+stream_copy_to_stream($in, $out, $end - $start + 1, $start);
+return true;
diff --git a/tools/ci/serve.sh b/tools/ci/serve.sh
index b847d2bc..3a967f10 100644
--- a/tools/ci/serve.sh
+++ b/tools/ci/serve.sh
@@ -40,8 +40,8 @@ game_maker_serve() {
   # game-maker-video, here a process beside the server.
   php "$root/tools/video-worker.php" "$root/data" >/tmp/video-worker.log 2>&1 &
   # Without workers the single-threaded dev server stalls: the editor fetches project and
-  # textures in parallel.
-  PHP_CLI_SERVER_WORKERS=8 php -S 0.0.0.0:8080 -t /srv >/tmp/php-server.log 2>&1 &
+  # textures in parallel. The router serves videos with Range requests, see there.
+  PHP_CLI_SERVER_WORKERS=8 php -S 0.0.0.0:8080 -t /srv "$root/tools/ci/router.php" >/tmp/php-server.log 2>&1 &
 
   for _ in $(seq 60); do
     curl -sf "${GAME_MAKER_BASE_URL}api/index.php?r=auth/session" >/dev/null 2>&1 && break