Thinking about using Xine, beside other players like VLC and the mplayer-based ones, I became interested in this and tried to understand this kind of terminology (player, frontend, gui, engine, etc), as they are used for example in the Xine-ui help:
For example, a question might be "is Totem a GUI/frontend of Gstreamer?"; but I do not want necessarily an answer to a such question here: but in order to create separate questions like "what video players are based on the X engine?" I need to know which are the main engines used by Ubuntu video players.