I already did a reinstall with pacman -R and then -S.
Now I tried inspecting the coredump. Its 249MB big (ulimit is at 500MB). But:
$ file core
core: ELF 64-bit LSB core file, x86-64, version 1 (SYSV), SVR4-style, from 'vlc pmpc_desktop.mp4', real uid: 1000, effective uid: 1000, real gid: 1000, effective gid: 1000, execfn: '/usr/bin/vlc', platform: 'x86_64'
$ gdb core
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"0x7ffe8074cc90s": not in executable format: file format not recognized
(gdb) bt
No stack.
(gdb)
Somethings up with the core file, but my latin ends here.