When you convert your video you can cut out the unnecessary parts of the video image. These can be the mattes or simply some of the areas of the image you do not need.
You can crop your video using the Crop source video option of the program Additional parameters. First you should select video to convert and the output video file name and folder. See the Converting Video to Flash section for more detail on that. After that enable the Crop source video option clicking it. The visual clippers will be added to your video:
Use the rectangles to resize the video image size. Click one of the rectangles with the mouse and, without releasing it, drag it to change the video image size. The same way the other video image dimensions are changed. Only the part of the video inside the clippers area will be left in the output video.
When you are ready, click the Start Conversion button to begin the conversion process.