How to Add Custom Cover Art to MKV Files

You can easily add a custom cover art image to an MKV (Matroska) video file, allowing compatible media players and file managers to display your preferred thumbnail or poster. This process does not require re-encoding the video; instead, the image is embedded directly into the file container as an attachment. This article explains how to do this quickly using free, widely-used tools like MKVToolNix and Mp3tag.

Understanding MKV Cover Art Requirements

The Matroska specification recognizes specific file names for cover art. To ensure your media player (such as VLC, Kodi, or Plex) displays the image correctly, you should follow these naming conventions:

• Portrait Cover (Standard): Name the image file cover.jpg or cover.png.
• Landscape Cover: Name the image file cover_land.jpg or cover_land.png.
• File Size: Keep the image resolution reasonable (e.g., 600x800 or 1000x1500 pixels) to avoid unnecessarily bloating the video file size.

Method 1: Using MKVToolNix (Recommended)

MKVToolNix is the official, open-source suite of tools for editing MKV files.

1. Download and install MKVToolNix.
2. Open the Multiplexer tool.
3. Drag and drop your MKV file into the “Source files” window.
4. Click on the Attachments tab (located in the middle section of the interface).
5. Right-click inside the “Attachments” box and select Add attachments, then select your custom cover art image.
6. Ensure the image is named exactly cover.jpg or cover.png in the “File name” column. If it is not, rename it within the tool.
7. Set the “MIME type” to image/jpeg or image/png (MKVToolNix usually detects this automatically).
8. Click the Start multiplexing button at the bottom of the window. A new MKV file will be created with the embedded cover art in just a few seconds.

Method 2: Using Mp3tag

While originally designed for audio files, Mp3tag also supports editing tags and cover art for MP4 and MKV video files.

1. Download and install Mp3tag.
2. Drag and drop your MKV file into the main Mp3tag window.
3. Click on the MKV file to select it.
4. In the left-hand metadata panel, right-click the empty disc icon/cover art placeholder and select Add cover…
5. Choose your custom image from your computer.
6. Click the Save icon (the floppy disk) in the top-left toolbar to write the image directly to the MKV file.