Video recording is the process by which visual images are recorded on some form of magnetic recording device such as tape or a video disc. In magnetic recording, an unrecorded tape is wrapped around a rotating drum that carries the tape through a series of steps before it leaves as a recorded tape.
The actual recording of the tape occurs on a cylindrical device known as the head. The head consists of a coil of wire wrapped around a core made of ferrite (iron oxide). When a camera is focused on a scene, the visual images it receives are converted to an electrical signal within the camera. That electrical signal passes into the recording head.
When the electrical signal reaches the recording head, it passes through the wire coil. When an electrical current passes through a metal coil, it creates a magnetic field. The strength of the magnetic field (called a flux) created depends on the strength of the electric current passing through the coil of wire. The strength of the electric current, in turn, depends on the intensity of the light received by the video camera. If the camera sees a bright spot, it produces a strong electric current, and the strong electric current produces a strong magnetic flux. When the camera sees a dim spot, it produces a weak electric current, and that weak electric current produces a weak magnetic flux.
The strength of the magnetic flux produced by the head is recorded on the magnetic tape that passes over it. The magnetic tape consists of millions of tiny pieces of iron oxide, like very tiny specks of flour. When the tape passes through a magnetic field, the iron oxide particles line themselves up in the direction of the magnetic field. If the field is very strong, all of the particles will line up in the same direction. If the field is very weak, only a small fraction of the particles will be aligned in the same direction. The brightness or dimness of the scene being photographed, then, is eventually translated into many or few iron oxide particles being lined up on the recording tape.
Magnetic tape is satisfactory for recording visual images under most circumstances. However, it does have certain disadvantages. One disadvantage is the time it takes to locate and play back any given portion of the recorded image. An alternative to using tape for recording images is a video disk.
A video disk is similar to a sound recording disk. It is a round, flat object covered with a thin layer of iron oxide. An incoming electrical signal is fed into recording heads posed above the rotating disk. As the signal is recorded on the disk, the recording heads move outward in a series of concentric circles away from the middle of the disk. Recording continues until the disk is filled.