diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..d645a26
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,133 @@
+name: Build
+
+on:
+  workflow_call:
+    inputs:
+      upload_artifacts:
+        required: false
+        type: boolean
+        default: false
+        description: 'Whether to upload build artifacts'
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        include:
+          - platform: windows
+            os: windows-latest
+            build_script: pnpm run build:win
+            ytdlp_asset: yt-dlp.exe
+            ytdlp_output: yt-dlp.exe
+            ffmpeg_url: https://github.com/yt-dlp/FFmpeg-Builds/releases/latest/download/ffmpeg-master-latest-win64-gpl.zip
+            ffmpeg_inner_path: ffmpeg-master-latest-win64-gpl\bin\ffmpeg.exe
+            ffmpeg_output: ffmpeg.exe
+          - platform: macos
+            os: macos-latest
+            build_script: pnpm run build:mac
+            ytdlp_asset: yt-dlp_macos
+            ytdlp_output: yt-dlp_macos
+            ffmpeg_arm_url: https://github.com/eko5624/mpv-mac/releases/download/2025-10-25/ffmpeg-arm64-defd5f3f64.zip
+            ffmpeg_x86_url: https://github.com/eko5624/mpv-mac/releases/download/2025-10-25/ffmpeg-x86_64-defd5f3f64.zip
+            ffmpeg_inner_path: ffmpeg/ffmpeg
+            ffmpeg_output: ffmpeg_macos
+          - platform: linux
+            os: ubuntu-latest
+            build_script: pnpm run build:linux
+            ytdlp_asset: yt-dlp
+            ytdlp_output: yt-dlp_linux
+            ffmpeg_url: https://github.com/yt-dlp/FFmpeg-Builds/releases/latest/download/ffmpeg-master-latest-linux64-gpl.tar.xz
+            ffmpeg_inner_path: ffmpeg-master-latest-linux64-gpl/bin/ffmpeg
+            ffmpeg_output: ffmpeg_linux
+    steps:
+      - name: Check out Git repository
+        uses: actions/checkout@v4
+
+      - name: Install Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 8
+
+      - name: Install Dependencies
+        run: pnpm install
+
+      - name: Download ffmpeg binary (Windows)
+        if: matrix.platform == 'windows'
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $ffmpegUrl = '${{ matrix.ffmpeg_url }}'
+          Invoke-WebRequest -Uri $ffmpegUrl -OutFile ffmpeg.zip
+          Expand-Archive ffmpeg.zip -DestinationPath ffmpeg -Force
+          $source = Join-Path 'ffmpeg' '${{ matrix.ffmpeg_inner_path }}'
+          $destination = Join-Path 'resources' '${{ matrix.ffmpeg_output }}'
+          Copy-Item -Path $source -Destination $destination -Force
+
+      - name: Download ffmpeg binary (macOS)
+        if: matrix.platform == 'macos'
+        shell: bash
+        env:
+          FFMPEG_OUTPUT: ${{ matrix.ffmpeg_output }}
+        run: |
+          set -euo pipefail
+          curl -L "${{ matrix.ffmpeg_arm_url }}" -o ffmpeg-arm.zip
+          unzip -q ffmpeg-arm.zip -d ffmpeg-arm
+
+          curl -L "${{ matrix.ffmpeg_x86_url }}" -o ffmpeg-x86.zip
+          unzip -q ffmpeg-x86.zip -d ffmpeg-x86
+
+          arm_bin="ffmpeg-arm/${{ matrix.ffmpeg_inner_path }}"
+          x86_bin="ffmpeg-x86/${{ matrix.ffmpeg_inner_path }}"
+
+          if [[ ! -f "$arm_bin" ]]; then
+            echo "::error::Missing arm64 ffmpeg binary at $arm_bin"
+            exit 1
+          fi
+          if [[ ! -f "$x86_bin" ]]; then
+            echo "::error::Missing x86_64 ffmpeg binary at $x86_bin"
+            exit 1
+          fi
+
+          lipo -create "$arm_bin" "$x86_bin" -output "resources/$FFMPEG_OUTPUT"
+          chmod +x "resources/$FFMPEG_OUTPUT"
+          rm -rf ffmpeg-arm ffmpeg-x86 ffmpeg-arm.zip ffmpeg-x86.zip
+
+      - name: Download ffmpeg binary (Linux)
+        if: matrix.platform == 'linux'
+        shell: bash
+        run: |
+          set -euo pipefail
+          curl -L "${{ matrix.ffmpeg_url }}" -o ffmpeg.tar.xz
+          mkdir ffmpeg
+          tar -xf ffmpeg.tar.xz -C ffmpeg
+          cp "ffmpeg/${{ matrix.ffmpeg_inner_path }}" "resources/${{ matrix.ffmpeg_output }}"
+          chmod +x "resources/${{ matrix.ffmpeg_output }}"
+
+      - name: Download yt-dlp binary
+        shell: bash
+        run: |
+          curl -L "https://github.com/yt-dlp/yt-dlp/releases/latest/download/${{ matrix.ytdlp_asset }}" -o "resources/${{ matrix.ytdlp_output }}"
+          if [[ "${{ matrix.platform }}" == "linux" ]] || [[ "${{ matrix.platform }}" == "macos" ]]; then
+            chmod +x "resources/${{ matrix.ytdlp_output }}"
+          fi
+
+      - name: Lint and format check
+        run: pnpm run check && pnpm run typecheck
+
+      - name: Build application
+        run: ${{ matrix.build_script }}
+
+      - name: Upload build artifacts
+        if: inputs.upload_artifacts == true
+        uses: actions/upload-artifact@v4
+        with:
+          name: dist-${{ matrix.os }}
+          path: dist/
+          retention-days: 1
+
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c82c2ba..70ce644 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,48 +5,5 @@ on:
     branches: [ main ]
 
 jobs:
-  test:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - os: windows-latest
-            build-script: pnpm run build:win
-            ytdlp-asset: yt-dlp.exe
-            ytdlp-output: yt-dlp.exe
-          - os: ubuntu-latest
-            build-script: pnpm run build:linux
-            ytdlp-asset: yt-dlp
-            ytdlp-output: yt-dlp_linux
-    runs-on: ${{ matrix.os }}
-
-    steps:
-      - name: Check out Git repository
-        uses: actions/checkout@v4
-
-      - name: Install Node.js
-        uses: actions/setup-node@v4
-        with:
-          node-version: 20
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-        with:
-          version: 8
-
-      - name: Install Dependencies
-        run: pnpm install
-
-      - name: Download yt-dlp binary
-        shell: bash
-        run: |
-          curl -L "https://github.com/yt-dlp/yt-dlp/releases/latest/download/${{ matrix.ytdlp-asset }}" -o "resources/${{ matrix.ytdlp-output }}"
-          if [[ "${{ runner.os }}" == "Linux" ]]; then
-            chmod +x "resources/${{ matrix.ytdlp-output }}"
-          fi
-
-      - name: Lint and format check
-        run: pnpm run check
-
-      - name: Build application
-        run: ${{ matrix.build-script }}
+  build:
+    uses: ./.github/workflows/build.yml
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 991dbe7..44c0348 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -6,57 +6,26 @@ on:
       - v*.*.*
 
 jobs:
+  build:
+    uses: ./.github/workflows/build.yml
+    with:
+      upload_artifacts: true
+
   release:
-    runs-on: ${{ matrix.os }}
-
-    strategy:
-      matrix:
-        include:
-          - os: windows-latest
-            build_script: pnpm run build:win
-            ytdlp_asset: yt-dlp.exe
-            ytdlp_output: yt-dlp.exe
-          - os: macos-latest
-            build_script: pnpm run build:mac
-            ytdlp_asset: yt-dlp_macos
-            ytdlp_output: yt-dlp_macos
-          - os: ubuntu-latest
-            build_script: pnpm run build:linux
-            ytdlp_asset: yt-dlp
-            ytdlp_output: yt-dlp_linux
-
+    needs: [build]
+    runs-on: ubuntu-latest
     steps:
       - name: Check out Git repository
         uses: actions/checkout@v4
 
-      - name: Install Node.js
-        uses: actions/setup-node@v4
+      - name: Download artifacts
+        uses: actions/download-artifact@v4
         with:
-          node-version: 20
+          pattern: dist-*
+          merge-multiple: true
+          path: dist/
 
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-        with:
-          version: 8
-
-      - name: Install Dependencies
-        run: pnpm install
-
-      - name: Download yt-dlp binary
-        shell: bash
-        run: |
-          curl -L "https://github.com/yt-dlp/yt-dlp/releases/latest/download/${{ matrix.ytdlp_asset }}" -o "resources/${{ matrix.ytdlp_output }}"
-          if [[ "${{ runner.os }}" == "Linux" ]]; then
-            chmod +x "resources/${{ matrix.ytdlp_output }}"
-          fi
-
-      - name: Lint and format check
-        run: pnpm run check
-
-      - name: Build application
-        run: ${{ matrix.build_script }}
-
-      - name: release
+      - name: Release
         uses: softprops/action-gh-release@v1
         with:
           generate_release_notes: true
@@ -73,4 +42,3 @@ jobs:
             dist/*.blockmap
         env:
           GITHUB_TOKEN: ${{ secrets.ACCESS_TOKEN }}
-
diff --git a/.github/workflows/translator.yaml b/.github/workflows/translator.yaml
index 92c0a09..64d6ae6 100644
--- a/.github/workflows/translator.yaml
+++ b/.github/workflows/translator.yaml
@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: lizheming/github-translate-action
+      - uses: lizheming/github-translate-action@c55aac477e98562d4faed9f77c54ab8306ae6ebf
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 5976cec..9cef9f0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -58,6 +58,7 @@ src/
 - Build production bundles with `pnpm build`.
 - Create platform-specific artifacts with `pnpm build:win`, `pnpm build:mac`, or `pnpm build:linux`.
 - Use `pnpm build:unpack` to generate unpacked directories under `dist/` for manual inspection.
+- Bundle platform binaries of `yt-dlp` and `ffmpeg` under `resources/` (or set `YTDLP_PATH`/`FFMPEG_PATH`) before packaging so merges and audio extraction work out of the box.
 
 ## Working on Changes
 - Keep each pull request focused on a single problem or feature.
diff --git a/package.json b/package.json
index 32eb63e..e50d2d0 100644
--- a/package.json
+++ b/package.json
@@ -12,8 +12,9 @@
     "typecheck": "pnpm run typecheck:node && pnpm run typecheck:web",
     "start": "electron-vite preview",
     "dev": "node scripts/set-console-encoding.js && electron-vite dev",
-    "build": "pnpm run typecheck && electron-vite build",
-    "postinstall": "electron-builder install-app-deps",
+    "build": "electron-vite build",
+    "setup": "node scripts/setup-dev-binaries.js",
+    "postinstall": "node scripts/setup-dev-binaries.js && electron-builder install-app-deps",
     "build:unpack": "pnpm run build && electron-builder --dir",
     "build:win": "node scripts/check-ytdlp.js win && pnpm run build && electron-builder --win",
     "build:mac": "node scripts/check-ytdlp.js mac && pnpm run build && electron-builder --mac --x64 --arm64",
diff --git a/resources/.gitignore b/resources/.gitignore
index 7ae4548..6d02c3a 100644
--- a/resources/.gitignore
+++ b/resources/.gitignore
@@ -2,8 +2,11 @@
 yt-dlp.exe
 yt-dlp_macos
 yt-dlp_linux
+ffmpeg.exe
+ffmpeg_macos
+ffmpeg_linux
+ffmpeg
 
 # But keep the README
 !README.md
 !.gitignore
-
diff --git a/resources/README.md b/resources/README.md
index d485295..74d2506 100644
--- a/resources/README.md
+++ b/resources/README.md
@@ -48,8 +48,24 @@ Invoke-WebRequest -Uri "https://github.com/yt-dlp/yt-dlp/releases/latest/downloa
 Invoke-WebRequest -Uri "https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp" -OutFile "resources/yt-dlp_linux"
 ```
 
+## ffmpeg Binaries
+
+ffmpeg is required for merging audio/video streams and audio extraction. Bundle the matching binary for each target platform:
+
+### Required Files
+
+1. **Windows**: `ffmpeg.exe`
+2. **macOS**: `ffmpeg_macos`
+3. **Linux**: `ffmpeg_linux`
+
+### How to Download
+
+- **Windows / Linux**: Grab static builds from <https://ffmpeg.org/download.html> (or <https://github.com/yt-dlp/FFmpeg-Builds/releases>) and rename the binary to match the filenames above.
+- **macOS**: Download the `ffmpeg-arm64*.zip` and `ffmpeg-x86_64*.zip` assets from <https://github.com/eko5624/mpv-mac/releases/latest>. Extract them and merge into a universal binary with `lipo -create`, then save the result as `resources/ffmpeg_macos`.
+- On macOS/Linux ensure the final binary is executable: `chmod +x resources/ffmpeg_macos` (or `ffmpeg_linux`).
+
 ### Note
 
-- If you don't place binaries here, the app will attempt to download them at runtime
-- The app will automatically use the bundled version if available
-- File sizes: ~10-15 MB per binary
+- Bundled binaries are required for Windows builds. On macOS/Linux the app can also use ffmpeg/yt-dlp from the system PATH.
+- You can override the lookup paths via the `YTDLP_PATH` or `FFMPEG_PATH` environment variables if you prefer custom locations.
+- File sizes: ~10-15 MB per yt-dlp binary, ~40-80 MB per ffmpeg binary
diff --git a/scripts/check-ytdlp.js b/scripts/check-ytdlp.js
index dc284ff..ee9882f 100644
--- a/scripts/check-ytdlp.js
+++ b/scripts/check-ytdlp.js
@@ -3,38 +3,6 @@
 const fs = require('node:fs')
 const path = require('node:path')
 
-/**
- * Check if yt-dlp binary exists in resources directory
- * Usage: node scripts/check-ytdlp.js [platform]
- * Platform options: win, mac, linux
- * Exit with error code 1 if not found
- */
-function checkYtDlpExists(platform) {
-  const platformMap = {
-    win: 'yt-dlp.exe',
-    mac: 'yt-dlp_macos',
-    linux: 'yt-dlp_linux'
-  }
-
-  const filename = platformMap[platform]
-  if (!filename) {
-    console.error('❌ Error: Invalid platform specified!')
-    console.error('Usage: node scripts/check-ytdlp.js [win|mac|linux]')
-    process.exit(1)
-  }
-
-  const ytdlpPath = path.join(__dirname, '..', 'resources', filename)
-
-  if (!fs.existsSync(ytdlpPath)) {
-    console.error(`❌ Error: resources/${filename} not found!`)
-    console.error(`Please download ${filename} to the resources/ directory first.`)
-    console.error('You can download it from: https://github.com/yt-dlp/yt-dlp/releases/latest')
-    process.exit(1)
-  }
-
-  console.log(`✅ ${filename} found in resources/ directory`)
-}
-
 // Get platform from command line arguments
 const platform = process.argv[2]
 
@@ -44,5 +12,61 @@ if (!platform) {
   process.exit(1)
 }
 
-// Run the check
-checkYtDlpExists(platform)
+const supportedPlatforms = ['win', 'mac', 'linux']
+
+if (!supportedPlatforms.includes(platform)) {
+  console.error('❌ Error: Invalid platform specified!')
+  console.error('Usage: node scripts/check-ytdlp.js [win|mac|linux]')
+  process.exit(1)
+}
+
+const binaries = [
+  {
+    label: 'yt-dlp',
+    filenameMap: {
+      win: 'yt-dlp.exe',
+      mac: 'yt-dlp_macos',
+      linux: 'yt-dlp_linux'
+    },
+    help: {
+      default: 'https://github.com/yt-dlp/yt-dlp/releases/latest'
+    }
+  },
+  {
+    label: 'ffmpeg',
+    filenameMap: {
+      win: 'ffmpeg.exe',
+      mac: 'ffmpeg_macos',
+      linux: 'ffmpeg_linux'
+    },
+    help: {
+      win: 'https://ffmpeg.org/download.html',
+      linux: 'https://ffmpeg.org/download.html',
+      mac: 'https://github.com/eko5624/mpv-mac/releases/latest'
+    }
+  }
+]
+
+let hasMissingBinary = false
+
+for (const binary of binaries) {
+  const filename = binary.filenameMap[platform]
+  const binaryPath = path.join(__dirname, '..', 'resources', filename)
+
+  if (!fs.existsSync(binaryPath)) {
+    console.error(`❌ Error: resources/${filename} not found!`)
+    console.error(`Please download ${filename} to the resources/ directory first.`)
+    const help =
+      typeof binary.help === 'string' ? binary.help : binary.help[platform] || binary.help.default
+    if (help) {
+      console.error(`See ${help}`)
+    }
+    hasMissingBinary = true
+  } else {
+    console.log(`✅ ${filename} found in resources/ directory`)
+  }
+}
+
+if (hasMissingBinary) {
+  process.exit(1)
+}
diff --git a/scripts/setup-dev-binaries.js b/scripts/setup-dev-binaries.js
new file mode 100755
index 0000000..7ba6d4b
--- /dev/null
+++ b/scripts/setup-dev-binaries.js
@@ -0,0 +1,343 @@
+#!/usr/bin/env node
+
+/**
+ * Development environment setup script
+ * Automatically downloads yt-dlp and ffmpeg binaries based on the current system
+ */
+
+const fs = require('node:fs')
+const path = require('node:path')
+const os = require('node:os')
+const { execSync } = require('node:child_process')
+const https = require('node:https')
+const http = require('node:http')
+
+// Configuration
+const RESOURCES_DIR = path.join(__dirname, '..', 'resources')
+const YTDLP_BASE_URL = 'https://github.com/yt-dlp/yt-dlp/releases/latest/download'
+
+// Platform configuration
+const PLATFORM_CONFIG = {
+  win32: {
+    ytdlp: {
+      asset: 'yt-dlp.exe',
+      output: 'yt-dlp.exe'
+    },
+    ffmpeg: {
+      url: 'https://github.com/yt-dlp/FFmpeg-Builds/releases/latest/download/ffmpeg-master-latest-win64-gpl.zip',
+      innerPath: 'ffmpeg-master-latest-win64-gpl/bin/ffmpeg.exe',
+      output: 'ffmpeg.exe',
+      extract: 'unzip'
+    }
+  },
+  darwin: {
+    ytdlp: {
+      asset: 'yt-dlp_macos',
+      output: 'yt-dlp_macos'
+    },
+    ffmpeg: {
+      // For development, download only the architecture matching current system
+      arm64: {
+        url: 'https://github.com/eko5624/mpv-mac/releases/download/2025-10-25/ffmpeg-arm64-defd5f3f64.zip',
+        innerPath: 'ffmpeg/ffmpeg',
+        output: 'ffmpeg_macos',
+        extract: 'unzip'
+      },
+      x64: {
+        url: 'https://github.com/eko5624/mpv-mac/releases/download/2025-10-25/ffmpeg-x86_64-defd5f3f64.zip',
+        innerPath: 'ffmpeg/ffmpeg',
+        output: 'ffmpeg_macos',
+        extract: 'unzip'
+      }
+    }
+  },
+  linux: {
+    ytdlp: {
+      asset: 'yt-dlp',
+      output: 'yt-dlp_linux'
+    },
+    ffmpeg: {
+      url: 'https://github.com/yt-dlp/FFmpeg-Builds/releases/latest/download/ffmpeg-master-latest-linux64-gpl.tar.xz',
+      innerPath: 'ffmpeg-master-latest-linux64-gpl/bin/ffmpeg',
+      output: 'ffmpeg_linux',
+      extract: 'tar'
+    }
+  }
+}
+
+// Utility functions
+function log(message, type = 'info') {
+  const icons = {
+    info: '📦',
+    success: '✅',
+    error: '❌',
+    warn: '⚠️',
+    download: '⬇️'
+  }
+  console.log(`${icons[type] || 'ℹ️'} ${message}`)
+}
+
+function ensureDir(dir) {
+  if (!fs.existsSync(dir)) {
+    fs.mkdirSync(dir, { recursive: true })
+  }
+}
+
+function downloadFile(url, dest) {
+  return new Promise((resolve, reject) => {
+    const protocol = url.startsWith('https') ? https : http
+    const file = fs.createWriteStream(dest)
+
+    protocol
+      .get(url, (response) => {
+        if (response.statusCode === 302 || response.statusCode === 301) {
+          // Handle redirect
+          file.close()
+          fs.unlinkSync(dest)
+          return downloadFile(response.headers.location, dest).then(resolve).catch(reject)
+        }
+
+        if (response.statusCode !== 200) {
+          file.close()
+          fs.unlinkSync(dest)
+          return reject(new Error(`Failed to download: ${response.statusCode}`))
+        }
+
+        response.pipe(file)
+        file.on('finish', () => {
+          file.close()
+          resolve()
+        })
+      })
+      .on('error', (err) => {
+        file.close()
+        fs.unlinkSync(dest)
+        reject(err)
+      })
+  })
+}
+
+function extractZip(zipPath, extractDir) {
+  const platform = os.platform()
+  ensureDir(extractDir)
+
+  if (platform === 'win32') {
+    // Use PowerShell Expand-Archive on Windows
+    try {
+      const zipAbsPath = path.resolve(zipPath)
+      const extractAbsDir = path.resolve(extractDir)
+      execSync(
+        `powershell -NoProfile -Command "Expand-Archive -Path '${zipAbsPath.replace(/'/g, "''")}' -DestinationPath '${extractAbsDir.replace(/'/g, "''")}' -Force"`,
+        { stdio: 'inherit' }
+      )
+    } catch (error) {
+      throw new Error(`Failed to extract zip: ${error.message}`)
+    }
+  } else {
+    // Use unzip command on macOS/Linux
+    try {
+      execSync(`unzip -q "${zipPath}" -d "${extractDir}"`, { stdio: 'inherit' })
+    } catch (error) {
+      throw new Error(`Failed to extract zip: ${error.message}`)
+    }
+  }
+}
+
+function extractTarXz(tarPath, extractDir) {
+  ensureDir(extractDir)
+  execSync(`tar -xf "${tarPath}" -C "${extractDir}"`, { stdio: 'inherit' })
+}
+
+function setExecutable(filePath) {
+  if (os.platform() !== 'win32') {
+    fs.chmodSync(filePath, 0o755)
+  }
+}
+
+function fileExists(filePath) {
+  return fs.existsSync(filePath)
+}
+
+// Main download functions
+async function downloadYtDlp(config) {
+  const { asset, output } = config.ytdlp
+  const outputPath = path.join(RESOURCES_DIR, output)
+
+  if (fileExists(outputPath)) {
+    log(`${output} already exists, skipping download`, 'info')
+    return
+  }
+
+  log(`Downloading ${asset}...`, 'download')
+  const url = `${YTDLP_BASE_URL}/${asset}`
+  const tempPath = path.join(RESOURCES_DIR, `.${asset}.tmp`)
+
+  try {
+    await downloadFile(url, tempPath)
+    fs.renameSync(tempPath, outputPath)
+    setExecutable(outputPath)
+    log(`Downloaded ${output} successfully`, 'success')
+  } catch (error) {
+    if (fs.existsSync(tempPath)) {
+      fs.unlinkSync(tempPath)
+    }
+    throw error
+  }
+}
+
+async function downloadFfmpegWindows(config) {
+  const { url, innerPath, output } = config.ffmpeg
+  const outputPath = path.join(RESOURCES_DIR, output)
+
+  if (fileExists(outputPath)) {
+    log(`${output} already exists, skipping download`, 'info')
+    return
+  }
+
+  log(`Downloading ffmpeg for Windows...`, 'download')
+  const tempZip = path.join(RESOURCES_DIR, 'ffmpeg-temp.zip')
+  const extractDir = path.join(RESOURCES_DIR, 'ffmpeg-temp')
+
+  try {
+    await downloadFile(url, tempZip)
+    log('Extracting ffmpeg...', 'info')
+    extractZip(tempZip, extractDir)
+
+    const sourcePath = path.join(extractDir, innerPath.replace(/\\/g, path.sep))
+    if (!fileExists(sourcePath)) {
+      throw new Error(`ffmpeg binary not found at ${sourcePath}`)
+    }
+
+    fs.copyFileSync(sourcePath, outputPath)
+    log(`Downloaded ${output} successfully`, 'success')
+
+    // Cleanup
+    fs.unlinkSync(tempZip)
+    fs.rmSync(extractDir, { recursive: true, force: true })
+  } catch (error) {
+    if (fs.existsSync(tempZip)) fs.unlinkSync(tempZip)
+    if (fs.existsSync(extractDir)) fs.rmSync(extractDir, { recursive: true, force: true })
+    throw error
+  }
+}
+
+async function downloadFfmpegMac(config) {
+  const arch = os.arch()
+  const ffmpegConfig = config.ffmpeg[arch === 'arm64' ? 'arm64' : 'x64']
+
+  if (!ffmpegConfig) {
+    throw new Error(`Unsupported architecture: ${arch}`)
+  }
+
+  const { url, innerPath, output } = ffmpegConfig
+  const outputPath = path.join(RESOURCES_DIR, output)
+
+  if (fileExists(outputPath)) {
+    log(`${output} already exists, skipping download`, 'info')
+    return
+  }
+
+  log(`Downloading ffmpeg for macOS (${arch})...`, 'download')
+  const tempZip = path.join(RESOURCES_DIR, 'ffmpeg-temp.zip')
+  const extractDir = path.join(RESOURCES_DIR, 'ffmpeg-temp')
+
+  try {
+    await downloadFile(url, tempZip)
+    log('Extracting ffmpeg...', 'info')
+    extractZip(tempZip, extractDir)
+
+    const sourcePath = path.join(extractDir, innerPath)
+    if (!fileExists(sourcePath)) {
+      throw new Error(`ffmpeg binary not found at ${sourcePath}`)
+    }
+
+    fs.copyFileSync(sourcePath, outputPath)
+    setExecutable(outputPath)
+    log(`Downloaded ${output} successfully`, 'success')
+
+    // Cleanup
+    fs.unlinkSync(tempZip)
+    fs.rmSync(extractDir, { recursive: true, force: true })
+  } catch (error) {
+    if (fs.existsSync(tempZip)) fs.unlinkSync(tempZip)
+    if (fs.existsSync(extractDir)) fs.rmSync(extractDir, { recursive: true, force: true })
+    throw error
+  }
+}
+
+async function downloadFfmpegLinux(config) {
+  const { url, innerPath, output } = config.ffmpeg
+  const outputPath = path.join(RESOURCES_DIR, output)
+
+  if (fileExists(outputPath)) {
+    log(`${output} already exists, skipping download`, 'info')
+    return
+  }
+
+  log(`Downloading ffmpeg for Linux...`, 'download')
+  const tempTar = path.join(RESOURCES_DIR, 'ffmpeg-temp.tar.xz')
+  const extractDir = path.join(RESOURCES_DIR, 'ffmpeg-temp')
+
+  try {
+    await downloadFile(url, tempTar)
+    log('Extracting ffmpeg...', 'info')
+    extractTarXz(tempTar, extractDir)
+
+    const sourcePath = path.join(extractDir, innerPath)
+    if (!fileExists(sourcePath)) {
+      throw new Error(`ffmpeg binary not found at ${sourcePath}`)
+    }
+
+    fs.copyFileSync(sourcePath, outputPath)
+    setExecutable(outputPath)
+    log(`Downloaded ${output} successfully`, 'success')
+
+    // Cleanup
+    fs.unlinkSync(tempTar)
+    fs.rmSync(extractDir, { recursive: true, force: true })
+  } catch (error) {
+    if (fs.existsSync(tempTar)) fs.unlinkSync(tempTar)
+    if (fs.existsSync(extractDir)) fs.rmSync(extractDir, { recursive: true, force: true })
+    throw error
+  }
+}
+
+// Main setup function
+async function setup() {
+  const platform = os.platform()
+  const config = PLATFORM_CONFIG[platform]
+
+  if (!config) {
+    log(`Unsupported platform: ${platform}`, 'error')
+    process.exit(1)
+  }
+
+  log(`Setting up development binaries for ${platform}...`, 'info')
+  ensureDir(RESOURCES_DIR)
+
+  try {
+    // Download yt-dlp
+    await downloadYtDlp(config)
+
+    // Download ffmpeg
+    if (platform === 'win32') {
+      await downloadFfmpegWindows(config)
+    } else if (platform === 'darwin') {
+      await downloadFfmpegMac(config)
+    } else if (platform === 'linux') {
+      await downloadFfmpegLinux(config)
+    }
+
+    log('Development environment setup completed!', 'success')
+  } catch (error) {
+    log(`Setup failed: ${error.message}`, 'error')
+    process.exit(1)
+  }
+}
+
+// Run setup
+if (require.main === module) {
+  setup()
+}
+
+module.exports = { setup }
diff --git a/src/main/download-engine/args-builder.ts b/src/main/download-engine/args-builder.ts
index a044635..0429dc0 100644
--- a/src/main/download-engine/args-builder.ts
+++ b/src/main/download-engine/args-builder.ts
@@ -14,7 +14,8 @@ export const resolveVideoFormatSelector = (options: DownloadOptions): string =>
       return 'bestvideo+none'
     }
     if (!audioFormat || audioFormat === 'best') {
-      return 'best'
+      // Use bestvideo+bestaudio to ensure video and audio are merged into a single file
+      return 'bestvideo+bestaudio'
     }
     return `bestvideo+${audioFormat}`
   }
@@ -53,7 +54,11 @@ export const buildDownloadArgs = (
 
   // Format selection
   if (options.type === 'video') {
-    args.push('-f', resolveVideoFormatSelector(options))
+    const formatSelector = resolveVideoFormatSelector(options)
+    args.push('-f', formatSelector)
+    // Let yt-dlp automatically choose the best merge format (mkv/webm/mp4)
+    // based on codec compatibility. Forcing MP4 can cause failures
+    // when codecs are incompatible (e.g., VP9+Opus requires mkv/webm)
   } else if (options.type === 'audio') {
     args.push('-f', resolveAudioFormatSelector(options))
   } else if (options.type === 'extract') {
diff --git a/src/main/index.ts b/src/main/index.ts
index ef117cf..3010655 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -7,6 +7,7 @@ import appIcon from '../../build/icon.png?asset'
 import { configureLogger } from './config/logger-config'
 import { services } from './ipc'
 import { downloadEngine } from './lib/download-engine'
+import { ffmpegManager } from './lib/ffmpeg-manager'
 import { ytdlpManager } from './lib/ytdlp-manager'
 import { settingsManager } from './settings'
 import { createTray, destroyTray } from './tray'
@@ -179,6 +180,15 @@ app.whenReady().then(async () => {
   // IPC services are automatically registered by electron-ipc-decorator when imported
   log.info('IPC services available:', Object.keys(services))
 
+  // Initialize ffmpeg
+  try {
+    log.info('Initializing ffmpeg...')
+    await ffmpegManager.initialize()
+    log.info('ffmpeg initialized successfully')
+  } catch (error) {
+    log.error('Failed to initialize ffmpeg:', error)
+  }
+
   // Initialize yt-dlp
   try {
     log.info('Initializing yt-dlp...')
diff --git a/src/main/lib/download-engine.ts b/src/main/lib/download-engine.ts
index 8c8b5fa..a9da7a3 100644
--- a/src/main/lib/download-engine.ts
+++ b/src/main/lib/download-engine.ts
@@ -12,7 +12,7 @@ import type {
   VideoFormat,
   VideoInfo
 } from '../../shared/types'
-import { buildDownloadArgs } from '../download-engine/args-builder'
+import { buildDownloadArgs, resolveVideoFormatSelector } from '../download-engine/args-builder'
 import {
   findFormatByIdCandidates,
   parseSizeToBytes,
@@ -21,6 +21,7 @@ import {
 import { settingsManager } from '../settings'
 import { scopedLoggers } from '../utils/logger'
 import { DownloadQueue } from './download-queue'
+import { ffmpegManager } from './ffmpeg-manager'
 import { historyManager } from './history-manager'
 import { ytdlpManager } from './ytdlp-manager'
 
@@ -496,6 +497,46 @@ class DownloadEngine extends EventEmitter {
 
     const args = buildDownloadArgs(options, downloadPath, settings)
 
+    // Check if format selector contains '+' which means video and audio will be merged
+    const formatSelector =
+      options.type === 'video' ? resolveVideoFormatSelector(options) : undefined
+    const willMerge = formatSelector?.includes('+') ?? false
+
+    const urlArg = args.pop()
+    if (!urlArg) {
+      const missingUrlError = new Error('Download arguments missing URL.')
+      scopedLoggers.download.error('Missing URL argument for download ID:', id)
+      this.updateDownloadInfo(id, {
+        status: 'error',
+        completedAt: Date.now(),
+        error: missingUrlError.message
+      })
+      this.queue.downloadCompleted(id)
+      this.emit('download-error', id, missingUrlError)
+      this.addToHistory(id, options, 'error', missingUrlError.message)
+      return
+    }
+
+    let ffmpegPath: string
+    try {
+      ffmpegPath = ffmpegManager.getPath()
+    } catch (error) {
+      const ffmpegError = error instanceof Error ? error : new Error(String(error))
+      scopedLoggers.download.error('Failed to resolve ffmpeg for download ID:', id, ffmpegError)
+      this.updateDownloadInfo(id, {
+        status: 'error',
+        completedAt: Date.now(),
+        error: ffmpegError.message
+      })
+      this.queue.downloadCompleted(id)
+      this.emit('download-error', id, ffmpegError)
+      this.addToHistory(id, options, 'error', ffmpegError.message)
+      return
+    }
+
+    args.push('--ffmpeg-location', ffmpegPath)
+    args.push(urlArg)
+
     const controller = new AbortController()
     const ytdlpProcess = ytdlp.exec(args, {
       signal: controller.signal
@@ -593,23 +634,81 @@ class DownloadEngine extends EventEmitter {
         // Generate file path using downloadPath + title + ext
         const title = videoInfo?.title || 'Unknown'
         const sanitizedTitle = title.replace(/[<>:"/\\|?*]/g, '_').substring(0, 50)
-        const extension =
-          options.type === 'audio' ? options.extractFormat || 'mp3' : actualFormat || 'mp4'
+
+        // Determine file extension based on download type and format
+        // yt-dlp automatically chooses the best merge format (mkv/webm/mp4)
+        // based on codec compatibility, so we should use actualFormat when available
+        let extension: string
+        if (options.type === 'audio') {
+          extension = options.extractFormat || 'mp3'
+        } else if (willMerge) {
+          // For merged files, yt-dlp auto-selects format (mkv/webm/mp4)
+          // Use actualFormat if available, otherwise default to mkv (most compatible)
+          extension = actualFormat || 'mkv'
+        } else {
+          extension = actualFormat || 'mp4'
+        }
+
         const fileName = `${sanitizedTitle}.${extension}`
         const finalOutputPath = path.join(downloadPath, fileName)
 
-        scopedLoggers.download.info('Generated file path for ID:', id, 'Path:', finalOutputPath)
+        scopedLoggers.download.info(
+          'Generated file path for ID:',
+          id,
+          'Path:',
+          finalOutputPath,
+          'Will merge:',
+          willMerge
+        )
 
         let fileSize: number | undefined
+        let actualFilePath = finalOutputPath
         try {
           const fs = await import('node:fs/promises')
+          // Try to find the actual file - yt-dlp may generate files with slightly different names
           const stats = await fs.stat(finalOutputPath)
           fileSize = stats.size
+          actualFilePath = finalOutputPath
         } catch (error) {
-          if (latestKnownSizeBytes !== undefined) {
-            fileSize = latestKnownSizeBytes
-          } else {
-            scopedLoggers.download.warn('Failed to get file size for ID:', id, error)
+          // If the expected file doesn't exist, try to find it by scanning the directory
+          try {
+            const fs = await import('node:fs/promises')
+            const files = await fs.readdir(downloadPath)
+            // Look for files matching the title pattern with the correct extension
+            const matchingFiles = files.filter((file) => {
+              const baseName = file.replace(/\.[^.]+$/, '')
+              const fileExt = file.split('.').pop()?.toLowerCase()
+              return (
+                (baseName === sanitizedTitle || baseName.startsWith(sanitizedTitle)) &&
+                fileExt === extension.toLowerCase()
+              )
+            })
+
+            if (matchingFiles.length > 0) {
+              // Use the most recently modified file if multiple matches
+              const fileStats = await Promise.all(
+                matchingFiles.map(async (file) => {
+                  const filePath = path.join(downloadPath, file)
+                  const stats = await fs.stat(filePath)
+                  return { file, path: filePath, mtime: stats.mtime, size: stats.size }
+                })
+              )
+              const mostRecent = fileStats.sort((a, b) => b.mtime.getTime() - a.mtime.getTime())[0]
+              actualFilePath = mostRecent.path
+              fileSize = mostRecent.size
+              scopedLoggers.download.info('Found actual file:', actualFilePath, 'Size:', fileSize)
+            } else if (latestKnownSizeBytes !== undefined) {
+              fileSize = latestKnownSizeBytes
+              scopedLoggers.download.warn('File not found, using estimated size:', fileSize)
+            } else {
+              scopedLoggers.download.warn('Failed to find file for ID:', id, error)
+            }
+          } catch (scanError) {
+            if (latestKnownSizeBytes !== undefined) {
+              fileSize = latestKnownSizeBytes
+            } else {
+              scopedLoggers.download.warn('Failed to get file size for ID:', id, scanError)
+            }
           }
         }
 
@@ -621,7 +720,7 @@ class DownloadEngine extends EventEmitter {
           status: 'completed',
           completedAt: Date.now(),
           fileSize,
-          format: actualFormat || undefined,
+          format: willMerge ? 'mp4' : actualFormat || undefined,
           quality: actualQuality || undefined,
           codec: actualCodec || undefined
         })
diff --git a/src/main/lib/ffmpeg-manager.ts b/src/main/lib/ffmpeg-manager.ts
new file mode 100644
index 0000000..08396c6
--- /dev/null
+++ b/src/main/lib/ffmpeg-manager.ts
@@ -0,0 +1,101 @@
+import { execSync } from 'node:child_process'
+import fs from 'node:fs'
+import os from 'node:os'
+import path from 'node:path'
+
+class FfmpegManager {
+  private ffmpegPath: string | null = null
+
+  async initialize(): Promise<void> {
+    this.ffmpegPath = await this.findFfmpegBinary()
+    console.log('ffmpeg initialized at:', this.ffmpegPath)
+  }
+
+  getPath(): string {
+    if (!this.ffmpegPath) {
+      throw new Error('ffmpeg not initialized. Call initialize() first.')
+    }
+    return this.ffmpegPath
+  }
+
+  private getResourcesPath(): string {
+    if (process.env.NODE_ENV === 'development') {
+      return path.join(process.cwd(), 'resources')
+    }
+    return path.join(process.resourcesPath, 'app.asar.unpacked', 'resources')
+  }
+
+  private async findFfmpegBinary(): Promise<string> {
+    const platform = os.platform()
+    const resourceCandidates: string[] = []
+
+    if (process.env.FFMPEG_PATH && fs.existsSync(process.env.FFMPEG_PATH)) {
+      console.log('Using ffmpeg from FFMPEG_PATH:', process.env.FFMPEG_PATH)
+      return process.env.FFMPEG_PATH
+    }
+
+    if (platform === 'win32') {
+      resourceCandidates.push('ffmpeg.exe')
+    } else if (platform === 'darwin') {
+      resourceCandidates.push('ffmpeg_macos', 'ffmpeg')
+    } else {
+      resourceCandidates.push('ffmpeg_linux', 'ffmpeg')
+    }
+
+    const resourcesPath = this.getResourcesPath()
+    for (const candidate of resourceCandidates) {
+      const fullPath = path.join(resourcesPath, candidate)
+      if (fs.existsSync(fullPath)) {
+        if (platform !== 'win32') {
+          try {
+            fs.chmodSync(fullPath, 0o755)
+          } catch (error) {
+            console.warn('Failed to set executable permission on ffmpeg binary:', error)
+          }
+        }
+        console.log('Using bundled ffmpeg:', fullPath)
+        return fullPath
+      }
+    }
+
+    if (platform === 'darwin') {
+      const commonPaths = ['/opt/homebrew/bin/ffmpeg', '/usr/local/bin/ffmpeg']
+      for (const candidate of commonPaths) {
+        if (fs.existsSync(candidate)) {
+          console.log('Using system ffmpeg:', candidate)
+          return candidate
+        }
+      }
+    }
+
+    if (platform === 'linux' || platform === 'freebsd') {
+      try {
+        const systemPath = execSync('which ffmpeg').toString().trim()
+        if (systemPath && fs.existsSync(systemPath)) {
+          console.log('Using system ffmpeg:', systemPath)
+          return systemPath
+        }
+      } catch (_error) {
+        // Ignore error and continue
+      }
+    }
+
+    if (platform === 'win32') {
+      try {
+        const output = execSync('where ffmpeg').toString().split(/\r?\n/)[0]
+        if (output && fs.existsSync(output)) {
+          console.log('Using system ffmpeg:', output)
+          return output
+        }
+      } catch (_error) {
+        // Ignore error and continue
+      }
+    }
+
+    throw new Error(
+      'ffmpeg not found. Bundle it under resources/ (asarUnpack) or set the FFMPEG_PATH environment variable.'
+    )
+  }
+}
+
+export const ffmpegManager = new FfmpegManager()
diff --git a/src/renderer/src/pages/Home.tsx b/src/renderer/src/pages/Home.tsx
index 882e4d5..4b21c76 100644
--- a/src/renderer/src/pages/Home.tsx
+++ b/src/renderer/src/pages/Home.tsx
@@ -76,18 +76,20 @@ const getQualityPreset = (settings: AppSettings): OneClickQualityPreset =>
 
 const buildAudioSelectors = (preset: OneClickQualityPreset): string[] => {
   if (preset === 'worst') {
-    return ['worstaudio', 'worst']
+    return ['worstaudio']
   }
 
   const abrLimit = qualityPresetToAudioAbr[preset]
-  return dedupe([abrLimit ? `bestaudio[abr<=${abrLimit}]` : undefined, 'bestaudio', 'best'])
+  // Remove 'best' fallback to ensure merging - only use 'bestaudio' variants
+  return dedupe([abrLimit ? `bestaudio[abr<=${abrLimit}]` : undefined, 'bestaudio'])
 }
 
 const buildVideoFormatPreference = (settings: AppSettings): string => {
   const preset = getQualityPreset(settings)
 
   if (preset === 'worst') {
-    return 'worstvideo+worstaudio/worst'
+    // Use worstvideo+worstaudio as fallback instead of 'worst' to ensure merging
+    return 'worstvideo+worstaudio'
   }
 
   const maxHeight = qualityPresetToVideoHeight[preset]
@@ -110,7 +112,8 @@ const buildVideoFormatPreference = (settings: AppSettings): string => {
       combinations.push(video)
     }
   } else {
-    combinations.push('best')
+    // Use bestvideo+bestaudio as fallback instead of 'best' to ensure merging
+    combinations.push('bestvideo+bestaudio')
   }
 
   return dedupe(combinations).join('/')