How to convert MP4 to MKV
- Drop your MP4 file.
- Adjust quality, resolution or bitrate if you want (defaults are optimized).
- Optionally set a start time and duration to trim.
- Click Convert, watch the progress and download your MKV file.
Why convert MP4 to MKV?
MP4 is excellent for sharing, uploading and playing video anywhere, but it has some limitations:
- Lossy compression
- Re-encoding reduces quality slightly
Converting to MKV gives you:
- Multiple audio and subtitle tracks
- Open and flexible
- High quality
MP4 vs MKV: side-by-side comparison
| Feature | MP4 | MKV |
|---|---|---|
| Full name | MPEG-4 Part 14 | Matroska Video |
| File extension | .mp4 | .mkv |
| Type | Video | Video |
| Compression | Lossy (H.264/H.265) | Depends on codec |
| Transparency | No | No |
| Animation / multi-frame | Yes | Yes |
| Introduced | 2001 | 2002 |
| Developed by | MPEG (ISO) | Matroska.org |
| MIME type | video/mp4 | video/x-matroska |
| Best for | sharing, uploading and playing video anywhere | movies and archives with subtitles |
What are MP4 and MKV files?
MP4 (.mp4)
MP4 is the most compatible video format today. Phones, YouTube, Facebook, WhatsApp and smart TVs all play MP4, usually with H.264 video and AAC audio.
MKV (.mkv)
MKV is a flexible open container that can hold many audio tracks and subtitles in one file. It is popular for movies and series, but many phones, TVs and editors cannot play it natively.
Tips for the best MKV results
- For phones and social media, MP4 (H.264 + AAC) is the safest choice for video and MP3 for audio.
- Very large files (over 1 GB) may exceed browser memory on phones; trim them or use a computer.
- Bookmark this page or install the app to convert MP4 files offline next time.
Private by design: how this converter works
Unlike typical online converters that upload your file to a remote server, this MP4 to MKV converter processes everything on your own device using FFmpeg compiled to WebAssembly — the same engine used by professional video tools. Your file is read into browser memory, converted, and offered back as a download — it is never sent to us.
- No upload wait — conversion starts instantly, even on slow mobile data.
- Private — safe for NID copies, certificates, bank statements and personal photos.
- No limits — no daily quota, no queue and no watermark.
- Offline-ready — once loaded, many tools keep working without internet.
Frequently asked questions
Is this MP4 to MKV converter free?
Yes — free, unlimited and without watermarks or sign-up.
Are my MP4 files uploaded to a server?
No. Conversion happens inside your browser on your own device, so your files stay private.
Will I lose quality converting MP4 to MKV?
MKV preserves the quality of your source file exactly — though it cannot restore detail already lost in the original MP4.
Can I convert several files at once?
Yes. Drop multiple files and download them individually or together as a ZIP.
Does it work on iPhone and Android?
Yes. It works in Chrome, Safari, Edge and Firefox on phones, tablets and computers. You can also install the site as an app.
What is the difference between MP4 and MKV?
MP4 (MPEG-4 Part 14) is lossy (h.264/h.265) and best for sharing, uploading and playing video anywhere, while MKV (Matroska Video) is depends on codec and best for movies and archives with subtitles.
Why does the first conversion take longer?
The FFmpeg WebAssembly engine (about 30 MB) is downloaded once and cached. Later conversions start immediately.