You absolutely can resize the media control after it is created.
GetBestSize() returns a wx.Size, which is a recommendation for what size
the MediaCtrl thinks you should set. It's still up to you to set the
size of the MediaCtrl using SetSize().
I personally don't use GetBestSize(). For me, the best size is
determined by a number of factors related to my application and user
configuration rather than the video itself. But that's just me.
David