VLC Media Player
VLC Media Player as Diagnostic Tool
The VLC Media Player is generally used only for displaying video programs, not ripping or converting (although it has some conversion capabilities). It is especially useful for checking the aspect ratio of a recently ripped and/or converted file because, at least by default, it automatically scales its display to the height and width of file being played.
The key settings are in the Tools menu and Video menu, indicated by the red arrows in the image above. In the Tools menu, click on Preferences, then make sure the box labeled "Resize interface to video size" is checked. In the Video menu, Zoom should be set to "1:1 Original," and Zoom and Aspect Ration should both be set to "Default." These are the usual defaults, unless they've been previously overridden.
With these settings, VLC will automatically scale it's display to match the characteristics of the input file, and black bars or their absence will quickly become visible. The VLC window can be resized, but if black bars are embedded in the file being played, there will be no way that resizing can eliminate the black bars.
The Tools menu can also be used to display information about the video file, including its height and width.