VLC is a free media tool that can be used to convert your AVI files to MKV. This program is available for Windows, Mac OS X, Linux, and Android. It is not just a media player but also a great dvd ripper and video conversion program that support many video file extensions.
The newer version of VLC 3.0 can support 4K or even 8K video files. So it is a good choice if you are looking for a free AVI to MKV converter.
Official site: https://www.videolan.org/
Here’s how:
Step 1: Download and install the VLC media player on your computer.
Step 2: To convert AVI files to MKV, install the program and go to the Media menu and select Convert/Save.
Step 3: From a new window, choose the +Add button and pick the AVI files you wish to convert. Once selected, click the Open button.
Step 4: Click on the arrow next to the Convert/Save button and choose to Convert to bring up a new window.