This is a FAQ for Mac users as below:
“Can anyone recommend a program for cropping WMV files?
I have received footage where the guy has filmed in 4:3 modes, but it seems the receiver records in widescreen or so.
So it has added in black borders to fill in the space on the left and right. I just want to crop those. Thanks.” (Video Help)

With the assistance of WMV Cropper for Mac, Mac users can crop WMV files easily. Mac WMV Cropper provides two sample ways for cropping unwanted and black side of WMV files on Mac: dragging the dotted line and setting the values in the box. You also can set aspect ratio for WMV movies on Mac.

How to crop WMV files with WMV Cropper for Mac?

1. Free download and run WMV Cropper for Mac.

2. Import WMV files
Click “ADD files” for importing WMV files to Mac WMV Cropper

3. Set cropping size for WMV
In “crop” interface, WMV Cropper for Mac gives you two ways to crop black and unwanted side of WMV movies: Drag the dotted line around WMV and set the values in each box “Left”, “Top”, “Right”, “Bottom” for cropping WMV video.
You also can set proper aspect ratio such as Original, Full, 16:9 or 4:3 for WMV movies from the drop list of “Zoom”.

4. Crop WMV Mac
Click "Convert" button, WMV files will be cropped on Mac OS.