The word codec is based on the contraction of "coding" and "decoding". A codec always comes with two functions, one is to encode, one is to decode. A codec either does video or audio. A combination of video and audio codecs is used to have both audio and video. DivX, XviD, 3ivX, Sigma are for examples all video codecs. Mp3 and Ogg Vorbis are audio codecs. The part that is of interest for StreamPlug® is only the encoding part, since SP has its own decoder.
Since a film is made of a encoded video stream and an encoded audio stream, there needs to be a container to encapsulate both. The encapsulation of a file is found in its extension : .avi, .rm. .ogm are all containers that have the ability to encapsulate several streams (usually two : one video, one audio).
Mpeg-4 is a standard. Although it is meant to be able to integrate any type of data (text, 3d, etc), it is only widely used for video so far. It is the most advanced of its type and represents the generation after mpeg-2. Codecs belong to a standard family. There are many different mpeg-4 codecs, but only one mpeg-4 standard. DivX and XviD both belong to the mpeg-4 standard. StreamPlug is compatible with all of the mpeg-4 family of codecs provided proprietary options are turned off during encoding for some of them.
Ogg Vorbis is both an encapsulation method and an audio codec using that encapsulation; the extension of such files is : *.ogg . Ogg is the encapsulation part of Ogg Vorbis and Vorbis is the audio codec. An ogg file can contain any type of video stream, e.g DivX, XviD, etc, and is usually renamed .ogm when it does for clarity purposes (It is possible to leave it as a .ogg). We use that classification and will call a video file a n ogm and an audio one an ogg.