Convert WebM to other formats

With ffmpeg

I think you should do this with ffmpeg.

To install, type these lines in terminal:

sudo apt install ffmpeg

now you have ffmpeg installed, you can convert webm to mp4 by this command:

ffmpeg -i input_filename.webm output_filename.mp4

Let's say you have your sample.webm file in your downloads folder and you want to generate the output to the same folder. You run this command:

ffmpeg -i ~/Downloads/sample.webm -qscale 0 ~/Downloads/sample.mp4

If you don't want to type this long command every time in your terminal you can create a little bash function to do it for you.

In terminal type nano ~/.bashrc scroll down to the bottom and insert:

webmTOmp4 () {
  ffmpeg -i "$1".webm -qscale 0 "$1".mp4
}    
mp4TOmp3 () {
  ffmpeg -i "$1".mp4 "$1".mp3
}

Now you can do: mp4TOmp3 GENUINE\ -\ Thleilaxu-k8hrEbXURzg and the script will convert and save your new file with the same name to the same folder.

I recommend you to download the FF Multi Converter.

have a look at this page :

FF Multi Converter

You can watch and convert videos using VLC.

Install VLC:

sudo apt install vlc

To convert videos, this article in Laptop Magazine recommends looking for the Convert/Save option in VLC's Media menu.