An annoying little thing with VLC: by default, when you launch a video, iTunes automatically pauses. It can quickly become irritating in certain cases, especially when you’re just checking images by playing videos. The option exists to modify this behavior, but it’s not straightforward.
You need to navigate to VLC’s Settings, Show All in the options, go to Interface, Main Interfaces, macosx, and scroll down in the window. There’s a field called ‘Control external music players‘ with a few options, including ‘Do nothing‘.
Mac OS X
Power Mac G3