MKVToolNix 101.0

MKVToolNix is one of those applications that can look complicated at first, but becomes incredibly useful once you understand what it actually does. It is a free and open source collection of tools for creating, editing, inspecting, splitting, merging, and manipulating Matroska files such as MKV and MKA.

Unlike conventional video editors, MKVToolNix generally does not try to re-encode your video. Its main strength is multiplexing, which means combining existing video, audio, subtitle, chapter, metadata, and attachment streams into a new Matroska container.

That makes it exceptionally useful for people who maintain large movie and TV collections.

What Is MKVToolNix?

MKVToolNix is a collection of command-line tools and a graphical interface for working with Matroska media files.

The main tools include:

mkvmerge for creating and combining Matroska files

mkvinfo for inspecting Matroska files

mkvextract for extracting tracks and other elements

mkvpropedit for modifying properties without remuxing the entire file

mmg and the modern MKVToolNix GUI for graphical workflows

The project supports Windows, macOS, and Linux.

What Makes MKVToolNix So Useful?

The biggest advantage is that you can manipulate the contents of an MKV file without having to re-encode the actual video.

For example, imagine you have a 30 GB movie with:

• One video track

• Three audio tracks

• Five subtitle tracks

• Multiple chapters

• Embedded fonts

You might want to remove two audio tracks and three subtitle tracks.

With a conventional video editor, this could involve unnecessarily processing the video.

With MKVToolNix, you can simply select the tracks you want to keep and create a new MKV.

The video can remain untouched.

That makes the operation dramatically faster than re-encoding.

Add and Remove Audio Tracks

This is probably one of the most common reasons people use MKVToolNix.

You can easily choose which audio tracks should remain in the final file.

For example, you could keep:

• Japanese DTS-HD MA

• English AAC

• And remove:

• French AC-3

• German AC-3

• Commentary

The original audio streams can be copied without conversion.

This is particularly useful for people maintaining movie collections where releases contain many unnecessary language tracks.

Subtitle Management

MKVToolNix is excellent for managing subtitles.

You can add external subtitle files to an existing video and configure properties such as:

• Language

• Track name

• Default track

• Forced track

• Hearing-impaired flag

• Subtitle track order

You can also remove unwanted embedded subtitles.

This makes it easy to customize a release without touching the actual video or audio.

Add External Subtitles

Suppose you have an MKV containing a movie but want to add an external .srt or .ass subtitle.

MKVToolNix can add the subtitle directly into the MKV container.

This is especially useful with ASS subtitles because fonts and other resources can also be embedded as attachments.

The resulting file becomes a self-contained package.

Embedded Fonts

Matroska supports attachments, and MKVToolNix can manage them.

This is particularly important for styled subtitles.

An ASS subtitle may rely on specific fonts to display correctly. You can add those fonts as attachments to the MKV so compatible media players can access them.

For anime and other heavily styled subtitle releases, this is a particularly useful feature.

Chapters

MKVToolNix provides extensive chapter support.

You can import chapters, create new chapters, edit existing chapter information, and control chapter metadata.

This is useful for movies containing:

• Opening chapters

• Scenes

• Episodes

• Commercial breaks

• Special features

You can also use chapter information when splitting files.

Splitting MKV Files

MKVToolNix can split a large Matroska file into multiple files.

Splitting can be performed based on different criteria, including timestamps, file sizes, and chapters.

This is useful when dealing with very large recordings or when you need to divide a long file into separate episodes.

Because the operation is based around the container rather than traditional video editing, it can often be completed without re-encoding the video.

Joining and Appending Files

MKVToolNix can also append compatible files.

For example, if a recording was split into multiple segments, compatible segments can be combined into a single Matroska file.

This is useful for combining video segments while preserving the existing streams rather than re-encoding everything.

There are some compatibility rules, so files aren't necessarily interchangeable simply because they contain the same video codec.

Metadata Editing

MKVToolNix gives you control over Matroska metadata.

You can modify things such as:

• Track names

• Languages

• Default flags

• Forced flags

• Display dimensions

• Track ordering

• Chapter metadata

• Segment information

This is particularly useful for cleaning up media libraries.

For example, you can turn a generic track name into something more descriptive such as:

Japanese DTS-HD MA 5.1

or

English Commentary

That makes the file much easier to manage in media servers and playback applications.

Header Editor

The header editor provides another way to modify certain properties of existing Matroska files.

Unlike a complete remux, some changes can be made directly to the existing file.

This can be extremely fast when you only need to adjust metadata or specific Matroska properties.

The feature is powerful, although users should understand what they are changing because low-level container modifications can affect compatibility.

MKVToolNix GUI

You don't have to use the command line.

The MKVToolNix GUI provides a graphical interface for most common operations.

You can drag a video into the application, inspect its tracks, choose what should be included, configure metadata, and start the multiplexing process.

For everyday use, the GUI is more than sufficient.

The command-line tools become particularly valuable when you need automation.

Command Line Tools

This is where MKVToolNix becomes especially powerful for advanced users.

The command-line utilities can be scripted and integrated into automated media-processing workflows.

For example, you can build scripts that:

Remove unwanted language tracks

• Add subtitles

• Rename tracks

• Set default tracks

• Split files

• Extract subtitles

• Extract audio

• Generate reports

• Process entire directories

This makes MKVToolNix a good fit for media servers and large collections.

mkvmerge

mkvmerge is arguably the most important tool in the entire package.

It takes video, audio, subtitle, chapter, and attachment streams and creates a Matroska file from them.

A typical workflow might be:

• Video from one file

• Audio from another file

• Subtitle from an external file

• Chapter information from another source

• Fonts as attachments

And mkvmerge combines everything into one MKV.

The original streams can be copied directly without re-encoding.

mkvinfo

mkvinfo is useful when you need to understand what is actually inside an MKV file.

It can expose information about:

• Tracks

• Codecs

• Languages

• Track IDs

• Chapters

• Attachments

• Segment information

• Timing information

This is particularly helpful when troubleshooting media files or preparing a command-line operation.

mkvextract

mkvextract does essentially the opposite of multiplexing.

It allows you to extract individual elements from an MKV.

For example, you can extract:

• Audio

• Subtitles

• Chapters

• Attachments

• Timecodes

• Tags

This is extremely convenient when you need a subtitle or audio track from a larger MKV without converting the entire file.

mkvpropedit

mkvpropedit is particularly useful when you only need to modify certain Matroska properties.

It can edit selected metadata without creating an entirely new MKV.

This can save considerable time when working with very large files.

For example, changing a track property on a 50 GB movie doesn't necessarily need to involve copying the entire 50 GB video stream again.

No Traditional Video Re-Encoding

This is probably the most important thing beginners should understand.

MKVToolNix is not primarily a video encoder.

If you want to convert H.264 into H.265, reduce bitrate, resize a video, or convert DTS to AC-3, MKVToolNix isn't the right tool.

It focuses on the container and its streams.

That distinction is important.

If you want to change the actual encoded video, use a tool such as FFmpeg or HandBrake.

If you want to rearrange, add, remove, or modify streams inside a Matroska container, MKVToolNix is often the better choice.

Excellent for Media Libraries

MKVToolNix is particularly useful for people who maintain large media collections.

For example, you can clean up downloaded releases before adding them to Jellyfin, Plex, or another media server.

You could:

• Remove unwanted languages

• Remove commentary tracks

• Add missing subtitles

• Set the correct default audio

• Set the correct default subtitle

• Rename tracks

• Add chapters

• Embed subtitle fonts

• Remove unnecessary attachments

The result is a cleaner and more predictable media library.

Performance

Because MKVToolNix can copy streams without re-encoding them, many operations are significantly faster than conventional video editing.

The actual speed depends heavily on storage performance, file size, and what operation you're performing.

A simple metadata modification can be almost instantaneous.

A full remux of a large movie still requires reading and writing the streams, so it can take considerably longer.

Even then, it is generally much faster than encoding the video again.

Pros

• Free

• Open source

• Windows support

• Linux support

• macOS support

• Excellent MKV support

• Powerful GUI

• Powerful command line tools

• No video re-encoding for normal multiplexing operations

• Fast remuxing

• Add and remove audio tracks

• Add and remove subtitles

• Subtitle metadata management

• Chapter management

• Track ordering

• Language configuration

• Default and forced flags

• Embedded font support

• Attachment management

• File splitting

• File joining

• Audio and subtitle extraction

• Metadata editing

• Excellent scripting capabilities

• Very mature project

• Active development

Cons

• Primarily focused on Matroska

• Not a conventional video editor

• Does not replace FFmpeg for video conversion

• Does not perform general-purpose video encoding

• The interface can feel intimidating for beginners

• Some operations require understanding codecs and container formats

• Remuxing still requires reading and writing the media data

Who Should Use MKVToolNix?

MKVToolNix is ideal for anyone who works with MKV files regularly.

It is especially useful for:

• Movie collectors

• Anime collectors

• Plex users

• Jellyfin users

• Media server administrators

• Video archivists

• Subtitle enthusiasts

• Content creators

• Power users

• System administrators

• Anyone managing large video libraries

If you frequently download or archive media files, MKVToolNix is one of those utilities that quickly becomes indispensable.

MKVToolNix vs FFmpeg

FFmpeg is considerably broader.

It can encode, decode, convert, filter, stream, record, and manipulate multimedia in many different formats.

MKVToolNix is much more focused.

If your task is:

"Convert this video to H.265"

Use FFmpeg.

If your task is:

"Remove the French audio track, add this subtitle, set Japanese as the default audio, and keep the original video untouched"

Use MKVToolNix.

They complement each other rather than directly replacing each other.

Final Verdict

MKVToolNix is one of the best utilities available for anyone who works with Matroska files.

Its greatest advantage is its focus. It doesn't try to be a complete video editor. Instead, it gives you extremely precise control over the contents and metadata of MKV and related Matroska files.

The ability to add or remove tracks, manage subtitles, configure chapters, edit metadata, extract streams, split files, and remux media without re-encoding makes it incredibly useful for maintaining a serious media library.

Its command-line tools make it even more powerful for automation, while the graphical interface keeps common tasks accessible to less technical users.

The only real downside is that beginners may initially find the terminology and interface overwhelming. Once you understand tracks, containers, codecs, languages, flags, and multiplexing, however, MKVToolNix becomes an exceptionally efficient tool.

If you regularly manage MKV files, MKVToolNix is one of the first applications you should install.