As I understand it is a known issue that IrfanView does not play videos correctly its first instance (reopening a second instance will play the video correctly).
This seems to be a bug in DirectShow under Windows 10, though I have no idea what kind of or how it leads to this strange behavior..

Anyway, of course it would be much more convenient if the workaround would not be needed.. I'm aware of the external player IV_Player plugin, but this is basically the same thing as the workaround, as it automatically opens a new window, which I would like to avoid.

So.. since this bug seems to be present for a while already, is there any known way by now to play back video normally in IrfanView under Windows 10?
For example, is it possible to make IV use a specific player, using its own display area?
Or is there any bugfix to that DirectShow bug, if so how do I update this?
Or, turning off DirectShow in IrfanView options, how to make it use the codecs I have installed? I have KLite Pack installed, but IrfanView still gives me the error "Windows can't play this file! (...) You can try install additional video/audio codes (...)" whenever I try to open a video.

Or does everyone under Win10 have the same issue and still no fix is known ( =( ) ?