MKVToolNix is the free open-source toolkit for rebuilding MKV files, letting you merge, split, retag and extract tracks without re-encoding, because it rewrites only the container and leaves the video and audio streams untouched.

MKVToolNix screenshots

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How to Download MKVToolNix

Pick your file - the one marked Recommended fits your device.
Main link goes to the developer's site - the file downloads straight from there.
Run the installer, or unzip the Portable file. Not starting? Try another server or a different browser.

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