Convert MKV to MP4 instantly in your browser - no upload needed
Repackage MKV files as universally supported MP4, without uploading them anywhere. MKV files are often large - and unlike server-based converters with 100 MB to 1 GB free caps, VidShift processes them locally in your browser, so there is no upload and no size limit beyond your own device.
or click to select a file
🔒 Your files never leave your device - 100% private & secure
Drag an MKV file onto the upload area or click Select Video. Even multi-gigabyte files load without an upload wait.
MP4 is selected automatically. Click Convert - compatible files remux losslessly in seconds. Download the MP4 when finished.
MKV (Matroska) is a flexible open container beloved by archivists and the home-media crowd because it can hold almost any codec, several audio tracks, chapters and rich subtitles all in one file. That flexibility is also its downside: iPhones, iPads, smart TVs, games consoles, most video editors and every web browser frequently refuse to open MKV files. MP4 is the safe, universal choice that plays everywhere, from a phone to a television to a slide deck.
Most MKVs carry H.264 or H.265 video with AAC or AC-3 audio, so conversion is usually a lossless remux: the streams are copied straight into an MP4 container with no re-encoding and no quality loss, which is why it often finishes in seconds even for a full-length film. When audio is stored as AC-3, which some browsers cannot decode, VidShift converts just the audio to AAC so the MP4 plays on the widest range of devices; if the browser cannot decode the audio track at all, you can still export a clean video-only MP4 rather than hitting a dead end.
The privacy angle matters more here than almost anywhere else. MKV files are frequently several gigabytes, and typical online converters either cap free uploads at 100 MB to 1 GB or make you wait through a slow, data-hungry transfer before they will even start. VidShift never uploads anything. Your file is read incrementally and processed locally, so a multi-gigabyte MKV converts without leaving your machine, without a size cap, and without tying up your bandwidth.
One honest caveat: MP4 supports a narrower set of subtitle and audio-track formats than MKV, so a file packed with many subtitle languages or exotic tracks may keep only what MP4 can carry. The video and primary audio always convert cleanly, which is what matters for the vast majority of playback.
No upload means no cap. The only limit is your device's memory, and large files stream through incrementally rather than loading fully into RAM, so multi-gigabyte MKVs are handled comfortably.
MP4 supports fewer subtitle formats than MKV. Text subtitle tracks that MP4 can carry are preserved where possible, while formats MP4 cannot store are dropped. The video and audio always convert cleanly.
When the codecs are MP4-compatible - usually H.264 or H.265 video - the streams are copied without re-encoding, so quality is identical. Only incompatible audio such as AC-3 is re-encoded to AAC.
No. Processing happens entirely in your browser using WebAssembly, so your MKV file never leaves your device. The tool even works offline after your first visit.