Directshow Filters for Ogg Vorbis, Speex, Theora, FLAC, and WebM, available from http://www.xiph.org/dshow/.

From their download page: "Before installation follow these steps: Uninstall any previous version of these filters. (This is important!)"

The installer is a WISE installer.

[edit] WPKG Package

<package id="oggcodec" name="Ogg Codec" revision="1" reboot="false" priority="0">
        <check type="uninstall" condition="exists" path="oggcodecs 0.71.0946" />
        <install cmd='"%PACKAGES%\oggcodecs_0.71.0946.exe" /S' />
        <upgrade cmd='"%PACKAGES%\oggcodecs_0.71.0946.exe" /S' />
        <remove cmd='"%PROGRAMFILES%\illiminable\oggcodecs\uninst.exe" /S' />
</package>

Note that in this version of the software at least, the uninstaller isn't silent, prompting "Are you sure you want to completely remove oggcodecs 0.71.0946 and all of its components?"