MKV2MP4 is an application that can convert video files in the MKV container format to more compatible MP4 video files. MKV2MP4 can convert most common MKV files very quickly, and has a queue for converting hundreds of files at once. MKV2MP4 can be configured to either produce files with perfect compatibility (at the expense of conversion speed) or to do conversion extremely quickly by producing files that are playable on most, but not all players (see F.A.Q.). Because MKV2MP4 doesn't re-encode the video track, conversion is fast and the resulting video has the exact same high video-quality as the source file. Note that most subtitles are supported (see F.A.Q.) but some players do not display them.
Note: The demo version is currently at 1.4.10; the version available for purchase is 1.4.15.