I have as script.
try set visible of windows of application "QuickTime Player" to not (visible of window 1 of application "QuickTime Player") end try
It does what I want, except that if QuickTime is not running when I run the script, QuickTime starts.
On starting QuickTime loads some advertising window, but (before the window is completly loaded) the script notes that visible of window 1 is false and does what it is supposed to.
Is there a way to test if QuickTime is running before I inquire about the visiblity of its windows?