Encode is a GUI for ffmpeg that can convert videos to a number of different formats. It includes typical video converter features like selection of video output format, audio output format, resolution, bitrate, sampling frequency and aspect ratio.
It also supports a youtube downloader and converter that can download high definition youtube videos and convert them. But you have to download a separate package for it.
Encode also supports video formats like mkv, webm and ogv. So if you use gtk-recoedmydesktop and want to convert .ogv file, it can do it for you.
Download Youtube Downloader (YAVTD) from here
There may be some missing dependencies when you install Encode. But the installer will automatically download and install them for you.