DevConverter converts your video files online. Amongst many others, we support MP4, WEBM and AVI. You can use the options to control video resolution, quality and file size.
MKV (Matroska video File) is a video container format that supports more than one audio and subtitle tracks at the same file. It is based on Extensible Binary Meta Language. It supports several video and audio compression formats. The difference between MKV file types with most other video extensions is that it is a container, not a codec.