Update locateFile to a fix critical bug in vite

src/bind/ffmpeg/bind.js

@@ -83,10 +83,42 @@ function reset() {
   Module["timeout"] = -1;
 }
 
+/**
+ * In multithread version of ffmpeg.wasm, the bootstrap process is like:
+ * 1. Execute ffmpeg-core.js
+ * 2. ffmpeg-core.js spawns workers by calling `new Worker("ffmpeg-core.worker.js")`
+ * 3. ffmpeg-core.worker.js imports ffmpeg-core.js
+ * 4. ffmpeg-core.js imports ffmpeg-core.wasm
+ *
+ * It is a straightforward process when all files are in the same location.
+ * But when files are in different location (or Blob URL), #4 fails because
+ * there is no way to pass custom ffmpeg-core.wasm URL to ffmpeg-core.worker.js
+ * when it imports ffmpeg-core.js in #3.
+ *
+ * To fix this issue, a hack here is leveraging mainScriptUrlOrBlob variable by
+ * adding wasmURL and workerURL in base64 format as query string. ex:
+ *
+ *   http://example.com/ffmpeg-core.js#{btoa(JSON.stringify({"wasmURL": "...", "workerURL": "..."}))}
+ *
+ * Thus, we can successfully extract custom URLs using _locateFile funciton.
+ */
+function _locateFile(path, prefix) {
+  const mainScriptUrlOrBlob = Module["mainScriptUrlOrBlob"];
+  if (mainScriptUrlOrBlob) {
+    const { wasmURL, workerURL } = JSON.parse(
+      atob(mainScriptUrlOrBlob.slice(mainScriptUrlOrBlob.lastIndexOf("#") + 1))
+    );
+    if (path.endsWith(".wasm")) return wasmURL;
+    if (path.endsWith(".worker.js")) return workerURL;
+  }
+  return prefix + path;
+}
+
 Module["stringToPtr"] = stringToPtr;
 Module["stringsToPtr"] = stringsToPtr;
 Module["print"] = print;
 Module["printErr"] = printErr;
+Module["locateFile"] = _locateFile;
 
 Module["exec"] = exec;
 Module["setLogger"] = setLogger;