MKVToolNix is the one of the best collection of tools (mkvmerge, mkvinfo, mkvextract, mkvpropedit and mmg) for modifying MKV files.

The graphical user interface (GUI) of the program allows you to manipulate Matroska (MKV) files in several ways.

You can use those tools to create, split, edit, mux, demux, merge, extract or inspect Matroska files.

MKVToolnix will also work with other video formats. Such as AVI, MPEG, MP4, MPEG, Ogg/OGM, RealVideo, MPEG1/2, H264/AVC, Dirac, VC1.

And more as well as some video codecs such as VP9 video codec support – reading from IVF, Matroska, WebM files, extract to IVF files.

Moreover the program can work with audio files such as AAC, FLAC, MP2, MP3, AC3, DTS/DTS-HD, Vorbis, RealAudio. And also work with most subtitle formats including SRT, PGS/ SUP, VobSub, ASS, and SSA.

It is a cross-platform application that will work on Microsoft Windows (both 32 and 64-bit versions), Apple macOS and Linux operating systems.

Here is also the portable version which does not require installation. You just need to start the function. It can also be stored on external devices and run on any computer you have access to.

# Version 103.0 “The Darkness” 2026-10-18

## New features and enhancements

* mkvmerge: AVC/H.264: the stereo mode is now set from the frame packing
arrangement SEI message in the video stream if neither the command line
nor the container specifies one. This works for MP4, Matroska, AVC
elementary stream and MPEG transport stream input and is already known
during file identification. Implements the AVC part of #6309.
* mkvmerge: HEVC/H.265: the stereo mode is now set from the frame packing
arrangement SEI message in the video stream if neither the command line
nor the container specifies one. This works for MP4, Matroska, HEVC
elementary stream and MPEG transport stream input and is already known
during file identification. Implements the HEVC part of #6309.
* MKVToolNix GUI: multiplexer: added new actions to the tracks context menu
for enabling/disabling all items belonging to the same source file as the
selected item. Implements #6318.

## Bug fixes

* mkvmerge: MP4 reader: fixed losing video frames at the end of the file due
to flushing the packetizers too early (when the first track ends instead of
only when all tracks in the file have ended). Another byproduct is that
`BlockDuration` attributes aren’t set for the last frame when they aren’t
needed anymore. Fixes #6320.
* MKVToolNix GUI: multiplexer: when identification fails due to an
unrecognized or unsupported format, clicking the “Cancel” button in the
error dialog shown no longer locks up the GUI in the state of
“identification is still running”, which disabled most elements. Fixes
#6298.
* MKVToolNix GUI: chapter editor: when adding chapters mandatory elements set
to their default values are removed in the underlying data structures. This
restores consistency to how the chapter editor worked when copying values
from the UI into them for the selected chapter. The result is that those
elements won’t show up in saved XML/Matroska files even if they have never
been selected in the UI. Fixes #6294.
* macOS: GUI: fixed check boxes in lists such as the multiplexer’s track list
being invisible on macOS 27 by patching the Qt bundled with the app. Patch
by corticalcode, based on the fix J.D. Purcell proposed in QTBUG-150017.
Fixes #6307.

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