In this video tutorial I show how to Crop a Video to 2.39:1 Cinema Style Widescreen Aspect Ratio using Sony Vegas Movie Studio HD Platinum 11.
I give you the measurements and instructions for 1080p, 720p, 480p and 360p video.
Because there are so many different types Aspect Ratios that are in use, there really is no "standard". I chose 2.39:1 to demonstrate this tutorial, but you could just have easily used 2.35:1 - basically there is no right or wrong - just personal preference.
Here is a link to an article on Wikipedia which explains the differences between all the Aspect Ratios used by the Film Industry and also talks about the history of the film industry: