On many occasions we need to convert a video to .OGV .MKV (Matroska) or .WEBM for our smartphone, to upload it to a website or for something else. Although we can do this using the terminal (with mencoder or ffmpeg), not everyone likes to always use commands and that is precisely why I am sharing this application 
With OggConvert They can convert to these three formats with a few simple clicks, just select the video you want to convert, select the format and voila (by default it converts to .ogv):
As you can see, it also allows us to define the sound and video quality.
But not only this, where it says Video format you can specify the codec to use (Theora, Dirac or VP8) and below if they click Advanced the option of File format, whereby they can change to.mkv either .webm
As you can see, a simple and easy to use application 
Well nothing more ... I hope this helps several.
regards