Convert MKV to MP4

Turn a Matroska file into MP4 in your browser: instantly if it already holds H.264, or re-encoded when it doesn't.

Drop your files here

.mkv, .mka, .webm · up to 300 MB

Choose files

First trackAll tracks

More settings

SubtitlesProcessing modeQualityAudio bitrate

How to Convert to MP4

1
Add your MKV file
MKV, MKA or WebM, up to 300 MB in the browser; larger H.264 files can go through Trim Video first without losing quality.
2
Choose the audio track and subtitles
Keep the first audio track or bring all of them along, and decide whether subtitle tracks get embedded, dropped or pulled out as separate SRT files.
3
Click Convert and download
An MP4 comes back in seconds if the video was already H.264, or after a full re-encode for VP9, AV1 or HEVC.

Why some MKV files convert instantly and others don't

Matroska is a container that can hold almost any video codec, unlike MP4, which only accepts a handful. When an MKV already carries H.264, converting it is pure repackaging: every frame is copied as-is, nothing is decoded, and a 100 MB file finishes in seconds with zero quality change. VP9, AV1 and HEVC don't fit inside MP4, so those get re-encoded to H.264 instead, at the quality setting you pick.

MKV carries more tracks than MP4 wants

A single Matroska file can hold a dozen audio tracks in different languages and just as many subtitle tracks. This tool keeps just the first audio track by default or brings every one of them along, tagging the first as default. Subtitles get the same choice: leave them out, convert them into MP4's native mov_text format, or extract every track as its own SRT file, bundled into a ZIP with the video.

ASS and SSA styling doesn't survive the trip

mov_text is the only subtitle format MP4 understands, and it carries plain text with timing, nothing else. A SubRip (SRT) track converts cleanly, but ASS or SSA subtitles with custom fonts and positioning lose that styling and come out as plain captions. Extracting subtitles as separate SRT files sidesteps the problem, since they stay outside the MP4.

Remuxed or re-encoded, always on your device

When the MKV already holds H.264, its streams are moved into an MP4 box in seconds without decoding a frame; VP9, AV1 or HEVC go through a full re-encode instead. Either way the work happens in this tab, nothing is uploaded, there is no account, and closing it clears everything.

Frequently asked questions

Does converting MKV to MP4 lose quality?

Only if the video inside isn't already H.264. An H.264 MKV is remuxed: every frame is copied as-is, with zero quality change. VP9, AV1 and HEVC have to be re-encoded, and the Quality setting controls how much detail that keeps.

Why did my MP4 end up with only one audio track?

MP4 supports multiple audio tracks just fine, but the default here keeps only the first one to match what most players expect. Switch the audio track option to "All tracks" before converting if you want every language or commentary track carried over.

How do I get the subtitles as separate files?

Set Subtitles to "Extract as SRT files" before converting. Every subtitle track in the MKV comes out as its own .srt file, packaged into a ZIP alongside the MP4.

What happens to ASS or SSA subtitle styling?

It's lost. MP4's native subtitle format only stores plain text and timing, so custom fonts, colors and on-screen positioning from ASS or SSA tracks don't carry over. Extracting the subtitles as SRT files instead keeps them usable outside the MP4, just as plain text.

What's the difference between remuxing and re-encoding?

Remuxing copies the video stream byte-for-byte into a new container in seconds, with no quality change, but it only works when the video is already H.264. Re-encoding decodes and rebuilds the picture from scratch, which is slower and governed by the Quality setting, but works on any codec MKV can hold.

Why does a VP9 or AV1 video inside my MKV get re-encoded?

MP4 cannot legally hold VP9 or AV1 video streams, so there's no way to just repackage them. The picture has to be decoded and rebuilt as H.264, which is the codec MP4 was built around.

What's the maximum file size?

Up to 300 MB in the browser. Files that already hold H.264 and only need remuxing can go through Trim Video first if they're larger, since that tool doesn't re-encode either.