spy on events from another app?

for example, open media player to play movie. i would like to catch event "window is mapped", "movie is finished", etc, and hang handler on it. it is interesting at least to know where such thing is more convenient to do: on Windows or Linux? And of course, if there is experience or any ideas, please share

Whichever the OS, there are some low-level events you might be able to observe (like window moved), but such high-level "events" like "movie is finished" are not something that the OS can tell you: the application itself has to notify you through whatever means. If it doesn't make these things public there's almost no way you could possibly react to something like this in a generic manner.