Maxell Corporation of America has nearly doubled the capacity of DVD media with its introduction of DVD+R Double Layer media, capable of storing up to 8.5GB of data or four hours of video.   In addition to four hours of DVD quality video, the new media has a capacity of 16 hours of VHS-quality video and one hour of high-definition-quality video on one side of the disc.  Unlike conventional DVD, double layer technology utilizes a laser with a variable focal length to encode and read the data on the disc. One focal length writes and reads to the top layers, while the other deals with the second layer, nearly doubling capacity.