A video codec is a complicated mathematical set of instructions that looks at each frame of a video and determines the best way to handle the redundant information during the compression phase, then determines how to reconstruct the information during the decompression phase (when somebody watches the video).
Some of the most common codecs are Sorenson, H.264, MPEG-1, MPEG-2, and MPEG-4.
A keyframe is a complete frame or picture with all of the data needed to display that frame.
The non-keyframe frames are called delta frames or P frames (for predictor frames).
Some codecs add a third type of frame called a bi-directional frame, which not only track the changes, but they compare themselves to the previous keyframe and to the delta frame after it to decide what they look like.
Video can be compressed for QuickTime and Windows Media through Final Cut Express and Adobe Premier Elements.
Video must be exported from Final Cut Express in order to be imported into iDVD to create a DVD. Adobe Premiere Elements allows you to create a DVD within the program itself without having to export the video.
Chapter points allow the viewer to navigate through the DVD at random. Menus allow you to access the chapter points and are created in both iDVD and Premiere Elements.
Once the DVD menu has been created and chapter points inserted, the video must be compressed to MPEG-2. MPEG-2 is the compression standard for DVDs.