I want code to right click context menu on a file and if it is a .mp4, then convert that to a .mp3 of the same name
also include an option to play faster by +25 +33 +50 or slower by -25 -33 -50 (in a sub menu)
I understand this is different depending on your system, so answer how to do it for the people who use the same system as you
some desktop environments and window managers have built in functionality to do this through something like config files or a gui config.
the intentionally "simplified" or "streamlined" alternatives (ie gnome) requires more involvement and runs at a gradient between simple kde like config file at one extreme end, to full on source modification at the other extreme end.
if something like this was a common thing for me; i would go with an environment that makes the bells and whistles available to you as the default option, like kde.