Convert video From 3gp to mkv

A 3GP file is a multimedia file saved in an audio and video container format developed by the 3rd Generation Partnership Project (3GPP). It stores video and audio streams transmitted between 3G mobile phones and over the Internet. Information from <a href='https://fileinfo.com'>FileInfo - The File Extensions Database</a>.

MKV file extension is a Matroska Video file. It's a video container much like MOV and AVI, but also supports an unlimited number of audio, picture, and subtitle tracks (like SRT or USF).