MKV → MP4

MKV to MP4 Converter — Free, In Your Browser

Drop an MKV file, get an MP4 you can play anywhere. When the video and audio inside are already H.264 and AAC, we just rewrite the container — no re-encoding, no quality loss, done in seconds.

  • No upload
  • No signup
  • No watermark
  • Fast remux when possible
  • Up to 500 MB

Files never leave your browser. The conversion runs locally on your device.

Why convert MKV to MP4 at all?

MKV (Matroska) is a flexible open-container format that can hold virtually any combination of video and audio codecs. That flexibility makes it popular with OBS recordings, Plex and Jellyfin media libraries, anime fansubs, and HDD video archives. The catch: most consumer devices, social platforms, and messaging apps expect MP4. Drop an MKV into iMessage, WhatsApp, Slack, Google Slides, or an iPhone Photos import, and it will either fail silently or refuse entirely. Converting to MP4 solves that without touching the picture quality.

Remux vs. re-encode — what actually happens

MKV is just a container. The video and audio streams inside it can already be H.264 and AAC — the exact codecs MP4 expects. When that is the case, this tool does a remux: it strips the MKV wrapper and writes the same streams into an MP4 container. No decoding, no encoding, no quality change — typically done in a few seconds regardless of file size. When the audio is FLAC, DTS, AC3, or another codec that MP4 players commonly reject, we re-encode only the audio track to AAC. The video is still copied untouched, so there is no visible quality loss. We also move the moov atom to the front of the file with +faststart so the MP4 starts playing immediately when streamed.

No upload — what does that mean?

Most online converters upload your file to their server, transcode it there, and hand you a download link. That is fine for a public clip, but a problem for a Plex recording of a family movie night, an internal OBS session, or any archive you would rather keep private. This tool runs FFmpeg inside your browser via WebAssembly. Your file never leaves your device — you can disconnect from the internet after the page loads and the conversion will still complete.

Where MKV files come from

The most common sources: OBS Studio saves screen and game recordings as MKV by default (because MKV is recoverable if the recording crashes — MP4 is not). Plex and Jellyfin media servers transcode or serve library files in MKV. Anime fansub groups release in MKV because it supports multiple audio tracks and subtitle streams. Blu-ray rips keep the MKV wrapper because it holds all the bonus audio tracks without loss. In every case the content is fine — only the wrapper needs to change for broad device compatibility.

Recording a screen capture instead?

If you are about to record and you know you will need MP4 at the end, save yourself the round-trip: Clipy records straight to a shareable link with no watermark and a viewer page that does not require a signup. You record, you get a link — no MKV, no conversion step, no format compatibility headache.

Common questions

Will my MKV lose quality when converted to MP4?

Almost never. When the inner video codec is H.264, we copy it byte-for-byte into the MP4 container — nothing is re-encoded. Audio is re-encoded to AAC only when the source uses a format MP4 players commonly reject (FLAC, DTS, AC3). That audio step is perceptually lossless at our 192 kbps default.

How long does it take?

For a standard OBS recording with H.264 video, a remux of a 1 GB file typically takes under 30 seconds in the browser. Files with audio that needs re-encoding take a bit longer because FFmpeg has to decode and re-encode that track, but the video still goes through at copy speed.

My MKV has multiple audio tracks or subtitles. What happens to them?

We map the first video and first audio track into the MP4 output. Secondary audio tracks, subtitle streams, and chapter markers are not carried over — MP4 can technically hold them, but most players ignore them anyway. If you need multi-track output, use HandBrake or mkvtoolnix on the desktop.

Is this really free?

Yes. No signup, no usage cap, no watermark, no Pro tier. The tool is part of Clipy's free toolset because we want people who land here for a one-off conversion to discover that Clipy is the screen recorder they were looking for in the first place.

How big a file can I convert?

About 500 MB in the browser, beyond which the WebAssembly memory ceiling becomes the bottleneck. For larger files — full-length movie rips, long OBS sessions, 4K archives — use a desktop converter like HandBrake or the Clipy desktop app.

Why does OBS save as MKV and not MP4 by default?

MKV is fault-tolerant: if OBS crashes mid-recording, the MKV file is still playable up to the point of the crash. MP4 writes its index at the end of the file — a crash before that step produces an unplayable file. OBS recommends remuxing to MP4 after recording, which is exactly what this tool does.

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