The black bars are there from the broadcasting feed to keep the 16:9 (widescreen) aspect ratio. That way, there isn't distortion (stretching) of the picture.
You can't really cap without them; you'll have to remove them manually from your caps after making them. You could use an image editing program like paint.net (I like it, and it's free), but that would be tedious doing them one at a time for your application.
Are you still using the Any2Jpeg program to convert your caps? If so, you can use the resize feature in that to crop them.
Resize using 640 for width and 360 for height. Tick the "Crop image to fit" button, and select "Center" from the drop-down menu.
Here's a screen shot of Any2Jpeg with an SD letterboxed cap. As you can see in the output preview, nothing from the picture is cut off or distorted, and the black bars are gone
Hope this helps!
