According to http://opensuse-guide.org/codecs.php, the codecs should be here:
http://opensuse-guide.org/repo/openSUSE_Leap_42.1/dvd
But this URL doesn’t work. Anyone know of an alternative?
No, you misinterpreted that.
The URL of the repo is http://opensuse-guide.org/repo/openSUSE_Leap_42.1/ (without “dvd”).
That page tells you to run:
zypper addrepo -f http://opensuse-guide.org/repo/openSUSE_Leap_42.1/ dvd
(note the space between the URL and “dvd”), which tells zypper to add that repo and give it the name “dvd”.
Also note that you cannot open that URL in a web browser. You need to add it as repo, normal access is not allowed.
Thanks clearing this up!