When we transfer VHS to DVD, our decks use the same basic operation of any VCR throughout history. No matter what brand a VCR is, it will have four common sections: an input section, a recorder section, a reader section, and an output section. These are tied together by the storage medium: the video tape itself.
The input section is controlled by whatever is sending A/V information into the VCR. For example, this could be a TV, cable signal, camcorder, or another VCR.
The recorder section handles VHS conversion, transferring all the input signals into a form that can be saved to tape. It writes or records the information onto the storage medium (on D-VHS, it writes VHS to digital). Conversely, the reader section interprets information that is stored on the video tape. For example, this might include television programs or sound signals. The reader converts the information into signals that are appropriate for the output unit.
The output section is the direct opposite of the input area. It is usually connected to a TV or another VCR. When we convert tapes to DVD, we output to a DVD recorder; when we convert video to AVI, the output it to a capture card.
Let’s look at how the recorder section works with the actual video tape (for example, when you copy VHS to VHS). A VCR video cassette holds brown tape that is similar to an audio tape. The tape is constructed from a long strip of plastic or mylar that is wound between two reels inside the plastic cassette shell. On one side of the tape, a material that can be magnetized is glued, usually an iron oxide mixed with an adhesive binder.
The tape is pulled around a cylinder in the VCR called a "head drum." The drum has tiny electromagnets called "heads" mounted on its surface. Electric signals from the audio and video of the recorder section are passed through coils of wire in these heads, which produce a tiny magnetic field that changes in respect to the audio and video signals.
When the tape passes around the drum in the recording section, the heads make contact with the oxide on the tape, thereby causing the tape to feel the magnetic field. The oxide becomes magnetized in direct proportion to the signal in the head. Since several heads are on the drum, multiple electric signals are converted to magnetic fields applied to the tape, thereby writing the audio or video information onto the tape, where it's stored for playback.
When you insert a tape to play it, gears, arms and other mechanisms pull the tape into the machine. The plastic tape is placed against read heads located in the drum cylinder. Subtle variations in this mechanism is why a time-base corrector is often useful when you record VHS to DVD.
The heads sense the energy fields located in the magnetic layer of tape. They then convert the magnetic fields into small electrical signals. The signals are amplified and sent to the output section, where a TV or similar device is responsible for converting the audio and video signals into light and sound.
It's that easy! When we copy video to DVD, our VHS VCRs, and that of any VHS to DVD service, use this same digital transfers process every time.