How to Convert MP4 to MKV Online
Follow these three simple steps to convert MP4 to MKV. No software installation required. Free and secure.
Select an MP4 Video
Choose the MP4 video you need to place in a Matroska container for an MKV-based player, library, or workflow.
Choose Video and Audio Settings
Keep the original resolution and frame rate or choose new values, then keep the automatic audio settings or select a sample rate and mono or stereo output.
Convert and Download
Start the conversion, review the original and output file sizes, and download the completed MKV video.
How Does the MP4 to MKV Converter Work?
The CompressFly MP4 to MKV converter decodes the MP4 source and re-encodes supported video as H.264 and available audio as AAC inside an MKV container. Conversion does not create new tracks, and subtitle streams are not copied to the output.
Conversion runs directly in your browser. Your MP4 video is not uploaded to a server, and the completed MKV file downloads from the browser to your device.
What "directly in your browser" means
- Your MP4 video is not uploaded to a server.
- Video conversion runs locally on your device.
- The completed MKV video downloads directly from your browser.
When to Convert MP4 to MKV
Create an MKV copy when a media library, player, or delivery specification explicitly uses the Matroska container.
Add Video to an MKV Library
Convert an MP4 file when your local media library or organizational workflow standardizes video as MKV.
Meet a Player Requirement
Create an MKV version for playback software or a device configuration that specifically requests Matroska video.
Provide an MKV Delivery Copy
Keep the original MP4 and make a separate MKV file for a recipient or system with a defined container requirement.
Related Video Tools
MP4 to MKV Converter FAQ
How do I convert MP4 to MKV online?
Use this online MP4 to MKV converter in three steps: 1. Select an MP4 video from your device. 2. Keep or change the available video and audio settings. 3. Start the conversion and download the completed MKV video.
What happens when I convert MP4 to MKV?
The converter re-encodes the MP4 video as H.264 and available audio as AAC, then stores the streams in a new MKV container.
Can I change the video resolution and frame rate?
Yes. Keep the source resolution and frame rate or select an available output resolution and frame rate before conversion.
Will converting MP4 to MKV make the file smaller?
Not necessarily. The output size depends on the source video, selected resolution, frame rate, audio settings, duration, and visual content. Use the Video Compressor when reducing file size is the main goal.
Is the MP4 to MKV converter free?
Yes. Convert MP4 to MKV for free with no registration or credit card required.
Is there a file size limit, and is my video uploaded?
Your video is processed locally in your browser and is not uploaded to a server, so there is no server upload limit. The practical limit depends on your device's available memory and processing power, as well as the video's duration and resolution.