I would like to easily be able to convert a MKV video to MP4 video in Ubuntu. Is there any way I can easily do this at all?
One easy way (requiring a terminal), is using FFMPEG.
First, open a terminal and install FFMPEG with this command:
sudo apt install ffmpeg
Now all you have to do to convert your video is this one single command:
ffmpeg -i <inputfile> <outputfile>
For example, in your case:
ffmpeg -i input.mkv output.mp4
FFMPEG will automatically detect/use the correct input and output formats.
Conversion may take a few minutes based on length and frame rate of video.