Well, of course.
If the server is not reachable, YaST cannot install those packages.
Can you reach that URL in a Webbrowser?
http://ftp.gwdg.de/pub/linux/packman/suse/openSUSE_13.1/
Works fine here btw.
You could of course try a different mirror:
http://packman.links2linux.de/mirrors
F.e. http://packman.inode.at/suse/openSUSE_13.1/ , I’m using that one and never had any problem.
Just enter YaST->Software Repositories and edit the URL there.
It seems that your VLC player can not support video codec that you can not play well. I alwaysconvert my videos to MP4/MOV format so that I can play the video smoothly on my Mac with QT or VLC player.