MKV to MP4 converter

How to use the mkv to mp4 converter

1. 01Choose your MKV file, or drop it onto the box.
2. 02Check the plan line: it says whether the file will convert without re-encoding, will re-encode to H.264 (and AAC for any sound), or will become a WebM file because your browser can't create MP4.
3. 03Click Convert to MP4.
4. 04Download the finished MP4.

What MKV files usually contain

MKV is the file extension for Matroska, an open container format designed from the outset to hold far more than a single video and audio stream: multiple audio tracks in different languages, multiple subtitle tracks, chapter markers and metadata can all sit inside one MKV file at once. That flexibility is exactly why MKV is a common choice for downloaded or ripped video, where several language and subtitle options are bundled together, rather than for straightforward camera or phone recordings.

Inside that container, the actual video and audio can be encoded in a wide range of codecs: H.264 and HEVC are common, but so are VP9, AV1 and older codecs depending on where the file came from. MP4 cannot hold every codec MKV can, so what an MKV converts to depends entirely on what is encoded inside it, not on the fact that it is an MKV.

Because of that range, two MKV files can behave completely differently when converted: one copies straight across in a moment, another needs a full re-encode. The plan line above the Convert button reflects your specific file rather than a generic answer for "MKV files".

Subtitles and extra audio tracks

This converter works on the primary video track and the primary audio track only: whichever video stream and whichever audio stream the file marks as its main ones are what get copied or re-encoded into the MP4. Any subtitle tracks in the MKV, and any additional audio tracks beyond the primary one, such as a second language or a commentary track, are not carried over into the output file.

This matters most for files that lean on MKV's ability to bundle several language tracks or subtitle options together: converting to MP4 collapses the file down to a single picture and a single soundtrack, the ones marked primary in the source. If you need a specific audio language, check which track the source file has marked as primary before converting, since that is the one that will carry through.

If a specific subtitle track matters for your use, keep the original MKV file alongside the converted MP4: the MP4 has no way to carry subtitles that were not already burned into the picture, so the source file remains the only copy that has them.

When the MKV has to be re-encoded

An MKV converts to MP4 without re-encoding only when its primary video track is H.264 or HEVC and its primary audio track is AAC or MP3, the codecs MP4 can hold directly. MKV commonly carries other codecs too, VP9 or AV1 video, or Opus, Vorbis or FLAC audio, none of which MP4 supports natively, and any of those trigger a re-encode instead.

Re-encoding decodes the primary video and audio fully and re-compresses them into H.264 and AAC, or into WebM if your browser cannot produce H.264, which takes noticeably longer than a remux and involves the same lossy trade-off as any other re-encode. It is unavoidable when the source codec is one MP4 cannot contain, and it needs your browser to decode that codec: if it cannot, the converter says so before you start.

The plan line tells you which situation you are in before you commit to converting: "Will convert without re-encoding", "Will re-encode to H.264 and AAC", or a note that your browser can't create MP4 and the tool will make a WebM file instead. There are no surprises about how long it will take or whether anything is being re-compressed.

Questions about the mkv to mp4 converter

Will MKV to MP4 lose quality?

Only if the primary video or audio codec inside your MKV is not one MP4 can hold directly. When it is H.264 or HEVC video with AAC or MP3 audio, the streams are copied across without re-encoding and nothing is lost; otherwise, provided your browser can decode it, the file is re-encoded, which is a lossy step.

Are subtitles kept?

No. This tool converts the primary video track and primary audio track only; subtitle tracks and any additional audio tracks in the MKV are not carried over into the MP4.

Why is my MKV not recognised?

Some MKV files use codecs this tool cannot read at all, rather than ones it simply has to re-encode; if a file fails to load, it is usually an unsupported codec inside the container rather than a problem with the MKV format itself.

Is my video uploaded?

No. The whole conversion runs in your browser; your MKV file, and the MP4 it becomes, never leave your device.

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Updated 22 September 2026 · All free tools