Surprisingly as it may be, Quicktime still doesn't natively support the Ogg Vorbis audio compression format. You need a plugin such as Quicktime FLAC to allow it the Apple media player to play Ogg Vorbis files.
Quicktime FLAC is very simple to set up and takes little space. Once installed, you can read any Ogg Vorbis file with Quicktime. Although Ogg Vorbis files are not as common as others like MP3 or AAC you can encounter one every once in a while. The quality will generally be the same as other popular audio formats, however it is attractive because it is truly open and unpatented.
Quicktime FLAC is still in Beta and hasn't been updated since 2004, so you can pretty much consider it abandoned, which means it's not guaranteed to work properly with the latest versions of Quicktime nor to always properly read Ogg Vorbis files. Choose one of the alternatives suggested at Vorbis.com to play any Ogg Vorbis file under Mac instead.
Quicktime FLAC is a plugin to play Ogg Vorbis files in Quicktime. Unfortunately it has not been updated since 2004 and remains in Beta.