You should know better then to say "transcoding to OGG". Ogg is the container, you can have almost any codec
At least the video codec often implies the audio codec, MPEG video usually has either an MPEG1 audio layer 2 or layer 3 (what we know as MP2 and MP3 audio). MPEG4 either uses the old MPEG1 audio or "AAC". "Ogg" Theora and Dirac both usually imply Vorbis for the audio layer, being the only general-purpose high-quality audio codec in the Ogg family.
But some containers like Matroska
are completely agnostic and if all you know is that a file is in "Matroska" format you really know nothing.
Even "Quicktime" has had many meanings (as a file format) over time. For many years it implied video encoded by a Sorenson codec, although just like Ogg and Matroska (and AVI etc) that's not the limit. Recently as the basic Quicktime container has become the official MPEG4 file format new Quicktime files are almost always MPEG4 or H.264 video, usually with AAC audio.
And now to see if I can drink this information out of my head.