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MKV to MP4Lossless MKV to MP4 converter
Convert MKV to MP4 without losing quality
Most MKV files already carry H.264 or H.265/HEVC video — codecs every MP4 player understands. This tool copies those streams into an MP4 container byte-for-byte, with no re-encoding and no quality loss. A two-hour movie converts in seconds.
Up to 20 files of 1.5 GB each per batch. No signup, no watermark, no upload — your videos stay on your device.
- Lossless remux
- No re-encoding
- Seconds, not minutes
- No upload
- 100% free
Files are processed on your device with FFmpeg compiled to WebAssembly — nothing is uploaded, logged, or stored.
How to convert MKV to MP4 without losing quality
Three steps — the key is a remux, not a re-encode.
Drop your MKV files into the converter
Drag and drop up to 20 MKV files (up to 1.5 GB each) into the zone above. On the first visit the browser downloads a one-time ~31 MB conversion engine and caches it for later.
The tool remuxes — no re-encoding, no quality loss
For H.264, H.265/HEVC, and AV1 video the tool performs a remux: it copies the compressed streams into the MP4 container byte-for-byte. Nothing is decoded or re-compressed, so the output is bit-identical to what was inside the MKV. Only the rare VP8/VP9 file triggers a re-encode, and the tool tells you which path it took.
Preview and download your lossless MP4s
Play any converted file right on the page to verify quality, then save files individually or grab all at once. Everything was processed locally — no upload, no server copy.
Remux vs re-encode: this tool vs HandBrake vs VLC
HandBrake and VLC are powerful, but both re-encode by default — which is slower and always loses some quality. If the goal is keeping quality intact, a remux is the right operation.
| This tool | HandBrake | VLC | |
|---|---|---|---|
| Default behaviour | Remux (lossless stream copy) | Re-encode (lossy) | Re-encode (lossy) unless you build a custom profile |
| Quality impact | Zero — bit-identical output | One generation of compression loss | One generation of compression loss (default mode) |
| Speed (2 GB file) | Seconds | 10–40 minutes | Minutes (re-encode) or seconds (manual stream copy) |
| Setup needed | None — open the page | Download + install app | Download + install app |
| Privacy | Local — nothing uploaded | Local | Local |
HandBrake and VLC are excellent tools for changing codecs, shrinking file size, or adjusting resolution. But when you only need to change the container — MKV to MP4 — a remux is faster and preserves every pixel.
MKV to MP4 quality — questions answered
Is the conversion truly lossless?
Yes — for H.264, H.265/HEVC, and AV1 video, which covers the vast majority of MKV files. The tool performs a remux: it takes the compressed video and audio streams out of the MKV container and places them into an MP4 container without decoding or re-compressing anything. The output file is bit-identical to the source — same resolution, same bitrate, same frame-by-frame data.
What is the difference between remuxing and re-encoding?
Remuxing copies the already-compressed streams from one container (MKV) to another (MP4). It takes seconds and changes zero pixels. Re-encoding decodes the video, then compresses it again with a new codec or settings — this is slow (minutes for a feature-length file) and always loses some information, even at the highest quality preset. This tool remuxes whenever the codecs allow it.
When does the tool have to re-encode?
Only when the MKV carries a video codec that MP4 players cannot handle — specifically VP8 or VP9. These are uncommon inside MKV files (most contain H.264 or H.265). When a re-encode is necessary, the tool labels the file clearly so you know the output went through one generation of compression.
Will the file size change?
For a remuxed file the size is virtually identical — typically within a few kilobytes of the original, because the compressed data is the same. The only difference is the container overhead, which is negligible. A re-encoded file may be slightly larger or smaller depending on codec settings.
Can I verify that no quality was lost?
Yes. The tool shows the conversion method (remux or re-encode) for every file. For remuxed files, you can compare the video bitrate and resolution of the source MKV and output MP4 with a tool like MediaInfo — they will be identical. You can also play the MP4 directly on the page to spot-check before downloading.
Do subtitles survive the lossless conversion?
Text subtitles (SRT, ASS/SSA) are converted to MP4's native timed-text format and preserved. Bitmap subtitles (PGS from Blu-rays, VobSub from DVDs) cannot be stored in an MP4 container, so those tracks are dropped while video and audio remain untouched.
Are my files uploaded anywhere?
No. The converter runs FFmpeg compiled to WebAssembly entirely inside your browser — there is no upload endpoint. Your files never leave your device, and conversions keep working even if you disconnect from the internet.
Is it free?
Completely free — no signup, no watermark, no daily limits. The site is supported by ads; the converter itself never asks for payment.
Why remuxing preserves quality
MKV and MP4 are containers — wrappers around compressed video and audio streams. The video inside an MKV is already compressed once (by x264, x265, or another encoder). Re-encoding unpacks that compression and repacks it, losing detail each time — the same way resaving a JPEG makes it blurrier.
Remuxing skips all of that. It takes the compressed data as-is and moves it into a new container. The output is the same bitrate, the same resolution, the same frame-by-frame data — just wrapped differently so that devices and editors that reject MKV can play it.
This tool uses FFmpeg compiled to WebAssembly and runs entirely in your browser. It inspects each file, picks the lossless remux path whenever the codecs allow it, and only falls back to re-encoding for the rare VP8/VP9 source. It is the same engine as the main MKV to MP4 converter — same 20-file batches, same 1.5 GB per-file limit, same privacy model.
Your videos never leave your device
Every conversion runs locally through WebAssembly FFmpeg. We never receive, store, or even see a byte of your video — there is no upload endpoint to send it to. Close the tab and nothing about your files persists anywhere.