Crops rows of pixels from the top of the YUV frames.
This function goes through all the frames in a video and crops the crop_height
top pixel rows of every frame.
Args:
yuv_file_name(string): The name of the YUV file to be cropped.
output_file_name(string): The name of the output file where the result will
be written.
width(int): The width of the original YUV file.
height(int): The height of the original YUV file.
crop_height(int): The height (the number of pixel rows) to be cropped from
the frames.