Convert MKV to MP4 Without Re-encoding

xFormat remuxes MKV files to MP4 in your browser, copying the video and audio without re-encoding when the codecs are MP4-compatible, so it is fast, lossless and nothing is uploaded.

Runs in your browser — files never leave your device.

How it works

MKV is great for storing video, but many phones, TVs, editors and websites want MP4. Here the conversion is usually a quick remux rather than a slow re-encode. Be aware that subtitles stored inside the MKV are not carried over to the MP4.

1
Select your MKV file.
2
Choose MP4 as the output format.
3
Click Convert and download the MP4.

Remuxing: the fast way to get an MP4

An MKV (Matroska) file often contains H.264 or H.265 video with AAC audio, streams an MP4 can hold as they are. In that case the converter lifts the streams out and puts them in an MP4 wrapper. Nothing is decoded, so there is no quality loss, and a long movie can take only moments.

If a stream does not suit MP4, for instance AC3 or DTS audio or VP9 video, that stream is re-encoded (H.264 video, AAC audio) while the compatible ones are still copied. If your browser cannot decode the codec at all, compatibility mode re-encodes the whole file. Either way that part is slower and slightly lossy.

What can get lost: subtitles and extra tracks

MKV can bundle several audio tracks, multiple subtitle tracks, chapters and attachments. MP4 is stricter, so the converter carries over only the main video track and the main audio track. Embedded subtitles (including styled ASS/SSA ones), extra audio languages, chapters and attachments are left out.

If subtitles matter, check the result in your player first, and keep the original MKV until you are sure. Burning subtitles into the picture is not something this tool does.

Large files

MKV rips are often big. Browsers need memory to process them, so aim for under about 500 MB on a desktop and about 200 MB on a phone. For larger files, a desktop browser with plenty of free RAM is your best bet.

Frequently asked questions

Can MKV be converted to MP4 without losing quality?

Yes, when the video and audio codecs are MP4-compatible, they are copied without re-encoding, so quality stays identical. If re-encoding is needed, a small loss is possible.

Will subtitles be kept when converting MKV to MP4?

No. Embedded subtitles and extra audio tracks are not carried over, so keep the original MKV if you need them.

Why is my MKV conversion so fast?

Because it is a remux: the streams are repackaged rather than decoded and re-compressed, which is mostly limited by how quickly your device can read and write the file.

Is my file uploaded to a server?

No. Processing happens locally in your browser, so the movie never leaves your device.

Does it work on a phone?

Yes, in mobile browsers, but keep files under about 200 MB because phones have less memory available to the browser.