Linux

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.

You got me curious, so I looked it up.
This isn't a "let me google that for you", it's an "I'm joining you on this journey".

https://develop.kde.org/docs/apps/dolphin/service-menus/
(KDE)

Looks like you drop a .desktop file into ~/.local/share/kio/servicemenus.
Name the file extensions, write your Exec= line, fill in a couple other details like what icon to use and what it should be called in the right-click menu, save it, and you're done.
I imagine it's similar in xfce.

Step 1) Install a file manager...

Which file browser are you using?

Are you using GNOME or KDE? I know those can definitely utilize shell scripts from the right click menu. I'd recommend grabbing FFMPEG (probably already have it) and SOX. You are going to need to create a pretty basic shell script that extract the audio as a wav using FFMPEG, changing the speed with SOX (you can use FFMPEG but I find the audio warping dog shit), then FFMPEG to convert to mp3. For both GNOME and KDE the context menu shortcuts typically only pass the path to file you have selected as an argument. So you'll need to create a script for each speed. Honestly, it's not gonna be easy. You might find something in the Dolphin (kde filemanager) settings that will enable some basic context menu scripts for converting video to mp3. If this is too intimidating then I would check github for an FFMPEG wrapper. It's the a/v swiss army knife in linux.