diff --git a/package-lock.json b/package-lock.json
index 167942a..72c64c4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17569,7 +17569,7 @@
     },
     "packages/ffmpeg": {
       "name": "@ffmpeg/ffmpeg",
-      "version": "0.12.1",
+      "version": "0.12.2",
       "license": "MIT",
       "dependencies": {
         "@ffmpeg/types": "^0.12.0"
diff --git a/packages/ffmpeg/package.json b/packages/ffmpeg/package.json
index d77e682..d7644fc 100644
--- a/packages/ffmpeg/package.json
+++ b/packages/ffmpeg/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@ffmpeg/ffmpeg",
-  "version": "0.12.1",
+  "version": "0.12.2",
   "description": "FFmpeg WebAssembly version for browser",
   "main": "./dist/umd/ffmpeg.js",
   "types": "./dist/esm/index.d.ts",
@@ -17,7 +17,8 @@
     "clean": "rimraf dist",
     "build:esm": "tsc -p tsconfig.esm.json",
     "build:umd": "webpack",
-    "build": "npm run clean && npm run build:esm && npm run build:umd"
+    "build": "npm run clean && npm run build:esm && npm run build:umd",
+    "prepublishOnly": "npm run build"
   },
   "files": [
     "dist",
diff --git a/packages/ffmpeg/src/const.ts b/packages/ffmpeg/src/const.ts
index 8ec2781..119ad23 100644
--- a/packages/ffmpeg/src/const.ts
+++ b/packages/ffmpeg/src/const.ts
@@ -5,7 +5,7 @@ export const CORE_VERSION = "0.12.1";
 export const CORE_URL = `https://unpkg.com/@ffmpeg/core@${CORE_VERSION}/dist/umd/ffmpeg-core.js`;
 
 export enum FFMessageType {
-  LOAD = "load",
+  LOAD = "LOAD",
   EXEC = "EXEC",
   WRITE_FILE = "WRITE_FILE",
   READ_FILE = "READ_FILE",
diff --git a/packages/ffmpeg/src/errors.ts b/packages/ffmpeg/src/errors.ts
index 297e273..d7246c7 100644
--- a/packages/ffmpeg/src/errors.ts
+++ b/packages/ffmpeg/src/errors.ts
@@ -3,3 +3,6 @@ export const ERROR_NOT_LOADED = new Error(
   "ffmpeg is not loaded, call `await ffmpeg.load()` first"
 );
 export const ERROR_TERMINATED = new Error("called FFmpeg.terminate()");
+export const ERROR_IMPORT_FAILURE = new Error(
+  "failed to import ffmpeg-core.js"
+);
diff --git a/packages/ffmpeg/src/types.ts b/packages/ffmpeg/src/types.ts
index c613708..d95267b 100644
--- a/packages/ffmpeg/src/types.ts
+++ b/packages/ffmpeg/src/types.ts
@@ -22,13 +22,6 @@ export interface FFMessageLoadConfig {
    * @defaultValue `https://unpkg.com/@ffmpeg/core-mt@${CORE_VERSION}/dist/umd/ffmpeg-core.worker.js`;
    */
   workerURL?: string;
-  /**
-   * When `thread` is true, ffmpeg imports `ffmpeg-core.worker.js` and thus
-   * makes multi-threaded core work.
-   *
-   * @defaultValue `false`
-   */
-  thread?: boolean;
 }
 
 export interface FFMessageExecData {
diff --git a/packages/ffmpeg/src/worker.ts b/packages/ffmpeg/src/worker.ts
index a8c8eb2..38529bc 100644
--- a/packages/ffmpeg/src/worker.ts
+++ b/packages/ffmpeg/src/worker.ts
@@ -22,7 +22,11 @@ import type {
   FileData,
 } from "./types";
 import { CORE_URL, FFMessageType } from "./const.js";
-import { ERROR_UNKNOWN_MESSAGE_TYPE, ERROR_NOT_LOADED } from "./errors.js";
+import {
+  ERROR_UNKNOWN_MESSAGE_TYPE,
+  ERROR_NOT_LOADED,
+  ERROR_IMPORT_FAILURE,
+} from "./errors.js";
 
 declare global {
   interface WorkerGlobalScope {
@@ -51,13 +55,17 @@ const load = async ({
   try {
     // when web worker type is `classic`.
     importScripts(coreURL);
-  } catch (e: unknown) {
+  } catch {
     // when web worker type is `module`.
-    if (e instanceof TypeError && e.toString().includes("Module scripts")) {
-      (self as WorkerGlobalScope).createFFmpegCore = (
-        (await import(coreURL)) as ImportedFFmpegCoreModuleFactory
-      ).default;
-    } else throw e;
+    (self as WorkerGlobalScope).createFFmpegCore = (
+      (await import(
+        /* @vite-ignore */ coreURL
+      )) as ImportedFFmpegCoreModuleFactory
+    ).default;
+
+    if (!(self as WorkerGlobalScope).createFFmpegCore) {
+      throw ERROR_IMPORT_FAILURE;
+    }
   }
 
   ffmpeg = await (self as WorkerGlobalScope).createFFmpegCore({
diff --git a/packages/util/package.json b/packages/util/package.json
index 54f838d..217c8f2 100644
--- a/packages/util/package.json
+++ b/packages/util/package.json
@@ -17,7 +17,8 @@
     "clean": "rimraf dist",
     "build:esm": "tsc -p tsconfig.esm.json",
     "build:umd": "tsc -p tsconfig.cjs.json && webpack",
-    "build": "npm run clean && npm run build:esm && npm run build:umd"
+    "build": "npm run clean && npm run build:esm && npm run build:umd",
+    "prepublishOnly": "npm run build"
   },
   "files": [
     "dist"