A high-definition, or HD, player and recorder works by converting analog audio and video signals into a digital format and storing this information by etching or burning it onto the surface of a disc with a laser. To record data, the analog signal passes through a circuit that converts the signal to digital binary code, a long string of zeros and ones that spirals outward from the center of the disc.
The laser emits pulses of light at the photo-sensitive disc surface that the recorder translates and stores as a pattern of “pits” for zeros when it detects the flash and “lands” for ones, when there is no flash. During playback, a motor guides the laser over the disc surface, and a sensor reads the reflections from the beam striking the disk, which scatters when it strikes a pit or a zero and reflects back when it strikes a land or a one. The sensor feeds this information to a digital to analog converter that converts the binary code back to an analog signal that is output through the television screen and speakers.
A standard DVD player uses a red laser with a 650 nanometer wavelength and increases the storage capacity of a 4.5-inch disc from 700 megabytes to 4.7 gigabytes. HD video must contain at least 1080 rows of pixels per frame, in contrast to the 480 rows required for standard definition video. To accommodate the need for additional storage space, HD players and recorders use a blue laser with a 405-nanometer wavelength that can read and write up to 25 gigabytes of data on a standard size disc.