Hello and thanks for the reply.
What are you trying to make (compile)? Attract mode?
Yes, as you can see from my link to the attract git wiki. I thought it obvious in this forum, but you're right, mentioning it wouldn't have hurt.
edit: It's the latest version 2.2.1-50.
Using Kubuntu you shouldn't have any problems..as it is just ubuntu..and thus supported.
I hope so, but although 14.04 has an EOS of 2019, many people have already moved on to 16.04, like the
Ubuntu PPA for mame >0.164 or the attract mode compiling instructions for Ubuntu I linked above. So, I fear that this error may occur only on 14.04, and that the attract devs only tested it on 16.04 as, like you said, "it is just Ubuntu". This is just a educated guess, though, from my experience as a 14.04 user in a growing 16.04-only world.
In case you wonder why I don't just upgrade to 16.04: KDE Plasma 5 still has too many issues for my taste, so I plan to skip 16.04 and hope that KDE is fully usable again by the next LTS 18.04. Until then, it's "never change a running system" for me.
Have you installed the restricted-extras package?
Yes, I have. I even tried to installed it (again) for safety's sake. Same error.