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ConvertBox

Video Converter

Convert video files online in your browser. Convert MP4, MOV, WebM, AVI, and MKV formats locally via FFmpeg.wasm. Free, secure, and no watermark.

Supported Formats

MP4

Best compatibility

WebM

Web optimized

AVI

High quality uncompressed

MOV

Apple optimized

MKV

Multi-track support

How to Use

  1. Upload the video you want to convert (MP4, MOV, WebM, AVI, or MKV — up to 50MB per file).
  2. Pick the target format by destination: MP4 (H.264) for social media sharing; WebM for lightweight web embeds; MOV for Apple editing suites.
  3. Click "Convert" — processing runs entirely in your browser via WebAssembly, the file never reaches an external server.
  4. The converted video downloads automatically, ready to import into CapCut, Premiere, DaVinci Resolve, or upload to social networks.
  5. For Reels, TikTok, or YouTube Shorts, use MP4 H.264 format at 1080×1920 vertical configuration.
  6. Converting iPhone MOV files to MP4 is highly recommended for compatibility with Windows, PowerPoint, or Android devices.

All processing is done in your browser, and files are never sent to a server.

Frequently Asked Questions

We support input and output conversion for MP4, WebM, AVI, MOV, and MKV video formats.
We utilize FFmpeg.wasm (FFmpeg compiled to WebAssembly). This lets your browser run video decoding and encoding locally without a backend server.
WebAssembly in browsers is restricted by a 32-bit address space, meaning it can only allocate up to 2-4GB of RAM. Processing videos larger than 50MB can easily crash the browser tab.
No. The entire translation and encoding happen client-side. The file never leaves your computer, ensuring complete privacy.
We use optimized compression parameters to maintain a balance between output quality and file size. However, some minor quality variance is standard in video transcoding.
Yes. If you wish to extract audio, you can use our dedicated Video to Audio tool, which extracts the sound as MP3/WAV.
Conversion speed is GPU and CPU dependent. Short 15-second clips typically convert in a few seconds, while longer videos near the 50MB limit may take up to a minute.
No. All operations are processed entirely inside your browser's local sandbox using client-side APIs (like WebAssembly, pdf-lib, or HTML5 Canvas). Your files and data never leave your device.
No. All tools on ConvertBox are 100% free. We do not insert watermarks, limit features, or require any registration or payment.
Yes. Once the page and its local library dependencies are loaded in your browser, the conversion logic runs completely offline without needing an active internet connection.

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