01
No Upload
FFmpeg runs via WebAssembly in your browser tab. Your file never touches a server.
CONVERTMP4FREE
FFmpeg runs 100% in your browser via WebAssembly. No file upload. No signup. No size limit. Private by design.
↓Drop your file below
// Converter
LOADING ENGINE
Initialising…
Why This
02
Real FFmpeg
Not a wrapper. Actual FFmpeg compiled to WASM — every codec, every flag.
03
Free Forever
No account. No watermarks. No throttling. No subscription.
04
Four Formats
MP4 → MKV, AVI, MOV, or re-encoded MP4. Stream copy = instant, lossless.
05
Custom Args
Pass any FFmpeg CLI argument. Full control over codec, bitrate, filters.
06
Live Logs
Watch FFmpeg output stream in real time. See exactly what is happening.
How It Works
- 01
Drop File
Drag and drop your MP4 file, or click to browse. Stays on your device.
- 02
Choose Format
Select MKV, AVI, MOV, or re-encoded MP4. Add custom FFmpeg args if needed.
- 03
Convert
Hit CONVERT. Watch the logs. File downloads automatically when done.
Formats
| Ext | Full Name | MIME | Best For |
|---|---|---|---|
| .mkv | Matroska Video | video/x-matroska | Best for archiving. Supports any codec, multiple audio tracks, subtitles, chapters. |
| .avi | Audio Video Interleave | video/x-msvideo | Maximum compatibility with older players and legacy software. |
| .mov | QuickTime Movie | video/quicktime | Native for macOS and iOS. Best for Apple ecosystem. |
| .mp4 | MPEG-4 Part 14 | video/mp4 | Re-encode with custom settings. Universally compatible. |
FAQ
- Is this free?
- Yes. No signup, no limits, no watermarks. Convert as many files as you want, forever free.
- Does my video get uploaded?
- No. Conversion happens entirely in your browser using FFmpeg WebAssembly. Your file never leaves your device — there are zero server uploads.
- What video formats can I convert?
- You can convert MP4, MKV, AVI, MOV, WebM, and virtually any video format. Output options include MKV, AVI, MOV, and MP4. Use custom FFmpeg args to target any format FFmpeg supports.
- How do I convert MKV to MP4?
- Drop your MKV file onto the converter, select MP4 as the output format, and click Convert. The conversion is instant — FFmpeg stream-copies the data with no quality loss.
- How do I convert MOV to MP4?
- Drop your MOV file, select MP4 as the output, and click Convert. iPhone MOV files (including HEVC/H.265) are fully supported.
- How fast is conversion?
- No upload wait — conversion starts immediately. Container-only changes (MP4 ↔ MKV, MOV → MP4) are near-instant. Re-encoding speed depends on your CPU and file size.
- Does converting video reduce quality?
- No — for container changes (MP4 to MKV, MKV to MP4, MOV to MP4), FFmpeg stream-copies the data unchanged. Zero quality loss. Re-encoding with custom parameters may reduce quality depending on your CRF setting.
- What is FFmpeg?
- FFmpeg is the world's leading open-source multimedia framework, used by YouTube, VLC, Chrome, and thousands of professional tools. This converter brings FFmpeg to your browser via WebAssembly — no installation needed.
- Which browsers work?
- Chrome, Firefox, and Edge are fully supported. Safari has limited SharedArrayBuffer support which FFmpeg.wasm requires, so results may vary.
- What are custom FFmpeg args?
- Advanced users can pass FFmpeg CLI arguments directly — controlling codecs, bitrate, resolution, and filters. Example to reduce file size: -c:v libx264 -crf 28 -preset fast -c:a aac
- Is there a file size limit?
- No imposed limit. Your browser RAM is the practical ceiling. For files over 2GB, ensure you have free memory. There are no server-side size restrictions.
Articles
All articles →4 min read
How to Convert MP4 to MKV Online Free — No Upload Needed
Step-by-step guide to converting MP4 to MKV in your browser using FFmpeg WebAssembly. Free, private, and instant.
4 min read
How to Convert MKV to MP4 Online Free — Instant Browser Conversion
Convert MKV to MP4 instantly in your browser using FFmpeg WebAssembly. Free, no upload, no software installation required.
4 min read
How to Convert MOV to MP4 Online Free — No Software Needed
Convert MOV to MP4 instantly in your browser. Free FFmpeg-powered converter — no file upload, no signup, works on any device.