diff --git a/package.json b/package.json
index e3e993c..359b85c 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@profullstack/player",
-  "version": "0.4.0",
+  "version": "0.4.1",
   "description": "One web player for every source a Profullstack site serves: MP4, HLS, MPEG-2 transport streams and audio, with one control bar, on desktop, mobile, PWA and television.",
   "keywords": [
     "video",
diff --git a/src/engines/mpegts.ts b/src/engines/mpegts.ts
index 4737c24..b8f810d 100644
--- a/src/engines/mpegts.ts
+++ b/src/engines/mpegts.ts
@@ -46,6 +46,15 @@ export interface MpegtsOptions {
   withCredentials?: boolean;
   /** Appended to a codec failure, e.g. "VLC can — the button is beside Play." */
   unplayableAdvice?: string;
+  /**
+   * Demux on a worker thread. Only set this on a **webpack** host.
+   *
+   * mpegts.js assembles its worker out of `__webpack_modules__`, so anywhere
+   * else the worker is broken — and broken asynchronously, which means no
+   * error, no fallback, and no playback at all. Defaults to false. See the
+   * note in `configFor`.
+   */
+  enableWorker?: boolean;
 }
 
 /**
@@ -73,19 +82,32 @@ export interface MpegtsOptions {
  * ever complained.
  */
 /** Exported for the test that pins these values; not part of the public API. */
-export function configFor(_isTv: boolean): Record<string, unknown> {
+export function configFor(_isTv: boolean, options: MpegtsOptions = {}): Record<string, unknown> {
   return {
     /*
-     * Demux on a worker thread.
+     * Off unless the host says otherwise, and the reason is not performance.
+     *
+     * Demuxing a broadcast-bitrate transport stream on the main thread competes
+     * with rendering the page it is playing on, so a worker looks like free
+     * performance. It is free only under webpack.
+     *
+     * mpegts.js builds its worker by STRINGIFYING `__webpack_modules__` --
+     * webpack's internal module registry -- in `utils/webworkify-webpack.js`.
+     * A Next.js host has that global and the worker works. A host bundling with
+     * Bun, esbuild, Vite or Rollup does not, and the worker it assembles is
+     * broken.
+     *
+     * It then fails in the worst available way. `Transmuxer` wraps the setup in
+     * a try/catch and falls back to inline transmuxing, but only a SYNCHRONOUS
+     * throw reaches that catch. A Worker that constructs from a blob whose body
+     * then fails is asynchronous: nothing throws, nothing falls back, no init
+     * segment ever arrives, and the player sits there having reported no error.
+     * Every stream simply does not play. That is what turning this on by
+     * default did to tipoffwatch, whose bundle Bun builds.
      *
-     * A transport stream at broadcast bitrate is real work, and doing it on the
-     * main thread means it competes with rendering the page it is playing on --
-     * which shows up as dropped frames rather than as an error. mpegts.js builds
-     * the worker from a blob URL, so a host serving a strict CSP needs
-     * `worker-src blob:` for this to take; without it the library falls back and
-     * the only thing lost is the contention it was avoiding.
+     * So it is opt-in, and only a host that knows it is webpack should opt in.
      */
-    enableWorker: true,
+    enableWorker: options.enableWorker ?? false,
 
     /*
      * Read ahead, on every screen.
@@ -159,7 +181,7 @@ export async function createMpegtsEngine(
     return { destroy: () => undefined, levels: () => [] };
   }
 
-  const config = configFor(isTv);
+  const config = configFor(isTv, options);
   let player: MpegtsPlayer | null = null;
   let stopped = false;
   let restarts = 0;
diff --git a/test/mpegts-config.test.ts b/test/mpegts-config.test.ts
index afa70d2..eb05f10 100644
--- a/test/mpegts-config.test.ts
+++ b/test/mpegts-config.test.ts
@@ -43,10 +43,30 @@ describe('the mpegts buffering profile', () => {
     expect(desktop.stashInitialSize).toBe(384 * 1024);
   });
 
-  it('demuxes off the main thread', () => {
-    // Broadcast-bitrate demuxing competes with rendering the page it plays on,
-    // and loses as dropped frames rather than as an error.
-    expect(desktop.enableWorker).toBe(true);
+  it('does NOT demux off the main thread unless the host opts in', () => {
+    /*
+     * A regression test with a real outage behind it.
+     *
+     * A worker reads like free performance, and it is -- under webpack only.
+     * mpegts.js assembles its worker by stringifying `__webpack_modules__`,
+     * webpack's internal module registry. A Next.js host has that global; a
+     * host bundling with Bun, esbuild, Vite or Rollup does not, and the worker
+     * it builds is broken.
+     *
+     * It fails silently, which is what makes it dangerous. `Transmuxer`'s
+     * try/catch only sees a SYNCHRONOUS throw, and a Worker that constructs
+     * from a bad blob fails asynchronously: nothing throws, nothing falls back
+     * to inline transmuxing, no init segment arrives, and the player reports no
+     * error. Every stream simply does not play. Turning this on by default did
+     * exactly that to tipoffwatch, whose bundle Bun builds.
+     */
+    expect(desktop.enableWorker).toBe(false);
+  });
+
+  it('lets a webpack host ask for the worker anyway', () => {
+    // The capability is real where the bundler supports it, so it stays
+    // reachable -- just never by default.
+    expect(configFor(false, { enableWorker: true }).enableWorker).toBe(true);
   });
 
   it('never pauses the download to idle', () => {