This tool is used to convert Matroska Multimedia Container (mkv) to Web Media (webm).

MKV is a free, open standard container format that can hold an unlimited number of video, audio, picture, or subtitle tracks in one file.

WebM is an audiovisual media file format. It is primarily intended to offer a royalty-free alternative to use in the HTML5 video and the HTML5 audio elements. It has a sister project WebP for images.