Free Online MKV to OGG Converter

MKV is an open source container that can contain media data compressed with a use of different codecs. It has a lot of advantages over the legacy AVI container: it can contain audio tracks and subtitles in different languages, that can be switched without stopping the playback, file seek and rewind are very fast. Also the format is easy to edit, that is why audio and video data can be extracted effortlessly.

This format is free, which apparently is one of the reasons for its popularity. The used codecs supports variable bit rates (as a default), and .ogg files usually play back easily on all platforms. All things being equal, the sound quality exceeds that of mp3 somewhat.