If you've ever needed to convert an MP4 file to MKV, you're not alone. MKV (Matroska Video) is one of the most flexible container formats available, and many media players, Plex servers, and editing tools prefer it over MP4.
The good news? You can convert MP4 to MKV without re-encoding — meaning zero quality loss — and you can do it entirely in your browser with FinalConvert.
Why Convert MP4 to MKV?
MP4 and MKV are both container formats — they wrap video and audio streams together. The key difference is flexibility:
| Feature | MP4 | MKV |
|---|---|---|
| Multiple audio tracks | Limited | ✅ Yes |
| Multiple subtitle tracks | Limited | ✅ Yes |
| Chapter support | Basic | ✅ Full |
| Compatibility | Very wide | Wide |
| File size | Same | Same |
MKV is the preferred format for:
- Home media servers (Plex, Jellyfin, Emby)
- Archiving video with multiple language tracks
- Storing videos with embedded subtitles
Does Converting MP4 to MKV Lose Quality?
No — if you use the same codec. Both MP4 and MKV are containers. The actual video data (encoded with H.264, H.265, etc.) stays identical when you just change the container. This is called a remux operation.
FinalConvert performs this conversion without re-encoding by default, so your video quality is 100% preserved.
Step-by-Step: Convert MP4 to MKV with FinalConvert
- Open FinalConvert at the homepage
- Drop your MP4 file into the drop zone (or click to select)
- Click the Format button in the tool panel
- Select MKV as the output container
- Keep the codec as-is (e.g., H.264) to avoid re-encoding
- Click Convert
- Download your MKV file when done
The entire process happens locally in your browser. Your file is never uploaded to any server.
What About File Size?
When converting MP4 to MKV without re-encoding, the file size stays virtually the same — sometimes a few kilobytes smaller due to container overhead differences.
If you want to reduce file size, you can optionally:
- Lower the quality setting (uses CRF encoding)
- Set a target output size in the Output Size tab
- Reduce resolution or frame rate
Common Questions
Can I convert MKV back to MP4?
Yes — the same process works in reverse. Just select MP4 as the output format.
Will subtitles be preserved?
FinalConvert focuses on video and audio streams. Embedded subtitle tracks may not be preserved in all cases.
How large can the input file be?
Since processing happens in your browser, the limit depends on your device's RAM. Most modern devices handle files up to several gigabytes without issues.
Conclusion
Converting MP4 to MKV is one of the simplest video operations you can do — especially when no re-encoding is needed. With FinalConvert, the whole process takes under a minute and your video quality stays perfect.