MKV to MP4

Why change the container

MKV (Matroska) is an open container that holds almost any codec, several audio tracks and subtitles; MP4 is the format phones, browsers, TVs and editors play everywhere. Both can carry the same H.264, H.265 or AAC streams, so moving a video from MKV to MP4 usually doesn't need re-encoding at all: the streams are copied into the new container and only the wrapping changes. That is why this converter is fast and lossless, and why the output is about the same size as the input.

It is the right tool when a player or editor refuses one container but supports the codecs inside it, or when you want MP4's features (universal playback on phones, browsers and TVs).

How it works here

The conversion runs entirely in your browser: the video is read from your disk in slices, its streams are copied into the new container and the result is saved back to your device. Nothing is uploaded, so there's no account, no daily limit and no size limit beyond your free disk space.

The file is read in slices in a Web Worker by Mediabunny, which demuxes the source and writes every video and audio packet unchanged into the new container. It only copies: a track the target can't hold is left out and named on the page, never re-encoded. Subtitle and data tracks are not carried over. The result is written to the browser's private file storage (Origin Private File System), so large files don't have to fit in memory, then offered for download. MKV output gets its duration and cues for seeking; MP4 output keeps its index at the end of the file, which every player reads.