For every one pixel in width, the output of the movie barcode generator can be uneven from top to bottom. One way to fix this problem is to use a program called ImageMagick to compress the png file down to one pixel in height and then resizing it back up to original size. When compressing down to 1 pixel in height, ImageMagick finds the average of all the pixels in that column. And thus at the end of the process, each pixel in a given column is the average of all the pixels originally in that column, resulting in a smoother looking barcode.
Assuming your input is 1280x480, this is what the command line input would look like:
convert *.png -resize 1280x1! -resize 1280x480! *.png
You can see the difference below.