This plugin is obsolete, unless you are using Directory Opus 8. For Opus 9 it has been replaced by the Audio Tags plugin.
Show tag information for Ogg Vorbis and FLAC audio files.
Author: Leo Davidson
Link: http://www.pretentiousname.com/ogg/
[Admin Note: I've consolidated several back-and-forth replies into a single post to keep the overall thread tidy. Each quote and response below was originally a separate post.]
My problem is still not fixed with the latest update, but I'd like to share a strange discovery.
If I rename any of my *.ogg files to *.flac, the Vorbis comments do appear correctly in the infotips. Which means that the plugin is definitely working, but the .ogg extension (which is present in the Music group) is not recognized by the plugin.
How odd is that?
By Jove, that did it 
I also pinpointed the culprit, which was the movie plugin. For some strange reason, if it's placed above the Ogg/Flac plugin, it will take precedence over it, although the ogg extension is definitely not listed in the "recognized filename extensions" (movie plugin settings).
Thanks Leo, and I hope it helps.
[quote="leo"]Something must have set PerceivedType = video under HKEY_CLASSES_ROOT.ogg on your system, as that will cause the movie plugin to handle a file without its extension being listed in the Movie plugin's configuration window.
It is very uncommon for .ogg files to contain video and there's also a separate .ogv extension for that. (It isn't common for the Ogg container format to be used for video at all, .ogv or not, FWIW. I don't think I've ever seen one and anyone likely to use Ogg as a container would probably use Matroska .MKV instead these days.)
Since .ogg is almost always used for audio I would say that whatever set its PerceivedType to Video in the registry (assuming my theory is correct) was asking for trouble.[/quote]
You nailed it right on the head.
Content Type = video/x-ogg
PerceivedType = video
That looks like the archeological remain of a long forsaken codec pack.
I believe the Vorbis video container is actually ogm. It was used quite a lot in anime fansubs a few years ago and I'm fairly sure it was supported by Matroska, CCCP or whatever anime codec I had back then. I'm exclusively using K-Lite nowadays, but that video/x-ogg type must somehow have survived unnoticed. I wiped it out and changed the perceived type accordingly.
Thanks for clearing that up 
The website says this plugin is already included in version 8. I have just installed 64-bit version 9 and the Ogg/FLAC plugin does not seem to be there. I see from another topic that the plugin for dMC is not available for 64-bit. Is Ogg/FLAC also not available for 64-bit?
Correct, the Ogg and RAW plugins have not yet been updated for x64.
UPDATE: There are x64 versions of them now.