Convert MKV videos to MP4 in the browser. Free, private, runs in your browser.
100% private — your files and text never leave your browser. All processing happens locally on your device.
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MKV is a flexible container that can hold many audio, video, subtitle, and attachment streams. MP4 is more widely supported but stricter. Convertful focuses on creating a playable MP4 from the primary audio and video streams, using remux when those streams are compatible and transcode when they need to be rewritten.
Some MKV features do not map cleanly into MP4. Subtitle tracks, fonts, attachments, chapters, or secondary audio streams may be skipped by this Phase 1 converter. If those tracks matter, keep the original MKV and check the output MP4 before sharing or archiving it.
The MKV is processed locally with FFmpeg.wasm after the app loads its static WebAssembly assets. Convertful does not upload the video, inspect the file on a server, or use a third-party media API.
Yes, when the MKV contains video and audio streams that MP4 can carry. Auto mode remuxes those streams without re-encoding; otherwise it transcodes locally for compatibility.
This browser converter focuses on the primary video and audio streams. Subtitle tracks, attachments, and unusual MKV features may be skipped if they cannot be represented safely in MP4.
No. The MKV is processed with the local FFmpeg WebAssembly engine in your browser, and the output MP4 is created on your device.
Remuxed output is usually close to the original size because streams are copied. Transcoded output can be smaller or larger depending on the source codec, CRF quality setting, and audio bitrate.
Some MKV files contain uncommon audio tracks or multiple audio streams. Try Transcode mode first; if audio is still missing, re-export the source with a standard AAC or MP3 audio track.