Win32, Windows Media Foundation. I have a media session (IMFMediaSession) playing some topologies. I get an IMFMediaEventGenerator from it and request async events by calling BeginGetEvent().

Question, when the async callbacks come, do they come on a worker thread, or on message boundaries? The main (UI) thread of the app is apartment threaded, if that’s relevant. I’d rather have it on threads.

If this is an implementation detail with no guarantee either way, I’d like to know that too.

Quick test seems to indicate – message boundaries. I could not mark the main thread as a multithreaded apartment, it would break things elsewhere.