Simple online media conversion

Convert MKV to MP4.

Change MKV video into MP4 for wider compatibility. H.264 plus AAC sources are remuxed; other codecs fall back to FFmpeg WASM.

Drop a video file here

or choose a file from your device

MP4 · MOV · WebM · MKV · AVI · M4V and more

How Justvert chooses a conversion path

Every file is inspected by the Media Analyzer, then the Strategy Engine picks COPY REMUX, WebCodecs or FFmpeg WASM. Compatible H.264 streams are copied. Hardware-friendly transcodes use the GPU. Legacy containers fall back to FFmpeg.

Change MKV video into MP4 for wider compatibility. H.264 plus AAC sources are remuxed; other codecs fall back to FFmpeg WASM.

Convert a video in three steps

No editing timeline, complicated settings or software installation. Just choose a file, select a format and convert.

01

Choose your file

Add a video from your device. Justvert can identify common video and audio formats automatically.

02

Pick an output format

Choose MP4 for compatibility, MP3 for audio, WebM for the web, or another format suited to your workflow.

03

Convert and save

Start the conversion, then save the finished file when it is ready. Processing stays in the browser.

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Convert MKV to MP4 FAQ

How do I convert MKV to MP4 online?

Open the MKV to MP4 converter, drop your MKV file, confirm the output is MP4, then choose Convert. Justvert processes the file in your browser and offers a download when it is ready.

Do I need to install an app to convert MKV to MP4?

No. This MKV to MP4 conversion runs in the browser. There is nothing to download or install.

Does Justvert upload my files to a server?

No. Conversion runs locally in your browser. The chosen file is read on the page, processed by remux, WebCodecs or FFmpeg WASM, then written back with a WritableStream or a download. Source files are not uploaded to a Justvert conversion server.

Will converting a video reduce its quality?

It can, if the file has to be re-encoded. Compatible H.264 plus AAC streams can be remuxed into MP4 without touching the pictures or the sound. WebCodecs and FFmpeg paths re-encode and may introduce some quality loss depending on the source and output size.

Is there a file size limit?

There is no fixed Justvert upload cap because files stay on your device. Very large files are limited by the memory available to the browser. If a conversion runs out of memory, try a shorter clip or a smaller output size such as 720p or 480p.

Can MKV become MP4 without re-encoding?

Yes, when the MKV already holds H.264 video and a compatible audio track such as AAC. Justvert remuxes those streams into MP4. Other codecs need a transcode.

What if my MKV has multiple audio tracks?

The converter writes a widely compatible MP4. Extra tracks or subtitle streams may be dropped so the file plays in ordinary players.