MKV and AVI are video packaging. Each video package type may contain different video codecs. The video format (codec required) may be or mpeg2, 3, or 4, as well as others. One simple way to standardize them is to transcode them with Handbrake
. Simply open Handbrake, choose the video file you want to transcode and click the start button. The default Handbrake output should work well for you. One of the cool things about handbrake is that it's available for Windows, Linux and MAC operating systems.