Convert MKV to MP4

Repackage an .mkv into an .mp4 that phones, TVs and editors accept. The picture is almost always copied unchanged; only incompatible audio gets re-encoded.

The converter is ffmpeg compiled to WebAssembly. It downloads once (30 MB) when you pick your first file, then stays in your browser cache.

Your file is processed by your own browser and never uploaded. The engine itself is a one-time 30 MB download the first time you use it, and after that it comes out of your browser cache.

How to use MKV to MP4

  1. 1Drop your .mkv onto the box above, or click to pick one.
  2. 2The tool reads what is inside. H.264 or HEVC video is copied as-is; audio that MP4 players choke on, like AC-3 or DTS, is converted to AAC.
  3. 3Download the .mp4 and check the row label to see exactly what was done.

What actually changes, and what does not

An MKV and an MP4 of the same movie can hold the exact same video stream. The difference is the box, not the contents, and this tool exploits that: when the video inside is H.264 or HEVC, which covers nearly every MKV in circulation, the stream is copied across untouched. No decoding, no generation loss, done in seconds.

Audio is where MKV's flexibility bites. MKV files frequently carry AC-3, DTS or FLAC tracks, and while MP4 can technically store some of these, the players people convert for cannot play them. So incompatible audio is re-encoded to AAC, the one codec every MP4 player on earth decodes. Re-encoding audio is fast, since it is a tiny fraction of the data, and the video stays untouched while it happens.

The honest trade-offs

Subtitle tracks are dropped rather than mangled; keep the MKV if you need them. Multiple audio tracks collapse to the first. And converting the container does not change the codec: an HEVC video in an MP4 still needs a device that decodes HEVC. That covers everything reasonably modern, but if your target is an older TV that only speaks H.264, use our video converter page and re-encode instead.

None of these caveats apply to the common case. A typical MKV goes in, an MP4 with an identical picture comes out a few seconds later, and the row tells you whether the audio was copied or converted.

Limits worth knowing

Files up to 500 MB are accepted, which fits episodes and clips but not a full Blu-ray remux. The work happens in your browser, so a laptop on battery will do it slower than a desktop. And the first file triggers a one-time download of the conversion engine, which the page discloses before it starts.

Frequently asked questions

Does MKV to MP4 conversion lose quality?
The picture almost never does. MKV files overwhelmingly contain H.264 or HEVC video, and MP4 holds both, so the video stream is copied byte for byte. Audio is the nuance, and the only part that may be re-encoded. AC-3 or DTS tracks become AAC so the result plays everywhere, which is a real but small change; stereo AAC at the bitrate used here is transparent on normal playback gear.
What happens to the subtitles?
They are dropped. MKV carries subtitles as proper text tracks, and MP4 has no equivalent that players reliably honour. Silently keeping them in a form nothing displays would be worse than saying this plainly, so keep your original MKV if the subtitles matter, or burn them in with desktop software first.
Why do players struggle with MKV in the first place?
MKV is a container built for flexibility. It can hold nearly any codec, any number of tracks, chapters and attachments, which is why the high-quality rip world loves it. That same flexibility is why hardware players and phones support it patchily. MP4 is the boring, universally implemented subset, and moving to it is exactly what this tool does.
My MKV holds several audio tracks. Which one is kept?
The first one. Browsers give this tool no track picker worth trusting across files, so it takes the default track, converts it if needed, and drops the rest. If you need a specific alternate language track, a desktop tool is the right instrument.
Is anything sent to a server?
No. The conversion runs entirely in your browser with ffmpeg compiled to WebAssembly. Your file never leaves your device.

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