not a dev, but arions answer suggest that onvideoformatchange has nothing to do with the aspect ratio (16:9, 4:3) but rather the video format (divx, xvid, ...) and the codec that is used for that type of video format when building the graph. But i might be wrong.
Ok, but what about introducing a new event just for that purpose? Would that be more acceptable?. That way at least no redundant graph rebuild is triggered.
I'm aware that this wasn't needed if all codecs were playing by the rules, but thats not always the case.
At leat in the case of mpc decoder this seems not true according to my testing. Thats the reason why i think, the tsreader should tell the renderer the aspect resolution directly(bypassing the filtergraph).[...]
I think graph rebuilding is the workaround that makes the badly behaving codecs to work correctly. [...]