Is there a size limit for MKV files?

There's no fixed limit, but because your own device does the encoding, very large files use a lot of memory and time. Short clips convert fastest.

Yes — the audio track is carried into the MP4 (re-encoded to AAC when a re-encode is needed).

Convert MKV to MP4

Convert Matroska MKV files to MP4 so they play on phones, TVs, and editors. Converted entirely in your browser — nothing is uploaded.

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Why convert MKV to MP4?

MP4 is the most widely supported video format there is. Converting from MKV fixes "unsupported file" errors on phones, social uploads, presentation software, and video editors.

How the conversion works

Matroska MKV files usually already contain H.264 video, so the tool first attempts a fast, lossless remux — copying the streams straight into an MP4 container. If the codecs aren't MP4-compatible, it automatically re-encodes to H.264/AAC.

Encoding happens on your device

Video encoding happens entirely in your browser using WebAssembly. There is no upload and no queue, but that also means your device does the work — expect a large or long clip to take a minute or more.

How to mkv to mp4

Drop your MKV file into the zone above.
Press Convert. Everything runs locally in your browser.
Download the MP4 when it's ready.

Related converters

Compress VideoShrink MP4 file size with a quality slider and resolution cap.MP4 to WebMTurn MP4 videos into open, web-friendly WebM (VP9/Opus).Trim VideoCut a clip to a start and end time without re-encoding.