OtsAV natively supports both widescreen (16:9) and legacy (4:3) displays. This ensures that all Video/CD+G images are displayed in their correct Aspect Ratio, so you won't see stretched or compressed images. This also means that if the source clip is recorded in 16:9 format, but the DVD is recorded in 4:3, OtsAV will fill a widescreen display with the correct aspect ratio image. Other video software doesn't take this into consideration, resulting in a thick black border around the entire video image.
If your second display is a legacy TV (4:3), set the video output aspect ratio accordingly, under the menu Options -> Video/CD+G -> Aspect Ratio (TV Type) -> 4:3.
Choose 16:9 mode for a widescreen TV under Options -> Video/CD+G -> Aspect Ratio (TV Type) -> 16:9.
Note: You don't need to change the Aspect Ratio settings for each clip being played. OtsAV will change how each clip is played, so that you always have a full screen image on your 2nd display. You only need to change the Output Aspect Ratio if you change the type of 2nd display you are using.
Tip: The Options -> Video/CD+G menu can also be accessed by right-clicking your mouse on the middle video display (when visible). This is the suggested method, as it is the quickest way to access the Video/CD+G features.