Press Flag x5 As with almost all cassette-based videotape systems, VHS machines pull the tape out from the cassette shell and wrap it around the inclined head drum which rotates at 1,800 rpm in NTSC machines and at 1,500 rpm for PAL, one complete rotation of the head corresponding to one video frame. VHS uses an "M-loading" system, also known as M-lacing, where the tape is drawn out by two threading posts and wrapped around more than 180 degrees of the head drum (and also other tape transport components) in a shape roughly approximating the letter M. The heads in the rotating drum get their signal wirelessly using a rotary transformer. Video recording For the process used to commercially make VHS tapes, see Print-through § Video recording. Panasonic Hi-Fi six-head drum VEH0548 installed on G mechanism as an example, demonstrated a typical VHS head drum containing two tape heads. (1) is the upper head, (2) is the tape heads, and (3) is the head amplifier. The upper- and underside of a typical four-head VHS head assembly showing the head chips and rotary transformer A typical RCA (Model CC-4371) full-size VHS camcorder with a built-in three-inch color LCD screen. The tape path then carries the tape around the spinning video-head drum, wrapping it around a little more than 180 degrees (called the omega transport system) in a helical fashion, assisted by the slanted tape guides.[40] The head rotates constantly at[a] 1798.2 rpm in NTSC machines, exactly 1500 in PAL, each complete rotation corresponding to one frame of video. Two tape heads are mounted on the cylindrical surface of the drum, 180 degrees apart from each other, so that the two heads "take turns" in recording. The rotation of the inclined head drum, combined with the relatively slow movement of the tape, results in each head recording a track oriented at a diagonal with respect to the length of the tape, with the heads moving across the tape at speeds higher than what would otherwise be possible. This is referred to as helical scan recording. A tape speed of 1+5⁄16 inches per second corresponds to the heads on the drum moving across the tape at (a writing speed of) 4.86[50][40] or 5.767 meters per second.[51][failed verification] The recording process in VHS consists of the following steps, in this order: The tape is pulled from the supply reel by a capstan and pinch roller, similar to those used in audio tape recorders. The tape passes across the erase head, which wipes any existing recording from the tape. The tape is wrapped around the head drum, using a little more than 180 degrees of the drum. One of the heads on the spinning drum records one field of video onto the tape, in one diagonally oriented track. The tape passes across the audio and control head, which records the control track and the linear audio track or tracks. The tape is wound onto the take-up reel due to torque applied to the reel by the machine.
Copying videotapes without the copyright owner's permission is illegal. An exception is made for libraries to replace a work that is lost or damaged if another copy cannot be obtained at a fair price [Section 108 of the Copyright Act of 1976]. Licenses may be obtained for copying and off-air recording. Absent a formal agreement, "Guidelines for Off-the-Air Recording of Broadcast Programming for Educational Purposes," an official part of the Copyright Act's legislative history, applies to most off-air recording: Videotaped recordings may be kept for no more than 45 calendar days after the recording date, at which time the tapes must be erased. Videotaped recordings may be shown to students only within the first 10 school days of the 45-day retention period. Off-air recordings must be made only at the request of an individual instructor for instructional purposes, not by staff in anticipation of later requests. The recordings are to be shown to students no more than two times during the 10-day period, and the second time only for necessary instructional reinforcement. The taped recordings may be viewed after the 10-day period only by instructors for evaluation purposes, that is, to determine whether to include the broadcast program in the curriculum in the future. If several instructors request videotaping of the same program, duplicate copies are permitted to meet the need; all copies are subject to the same restrictions as the original recording. The off-air recordings may not be physically or electronically altered or combined with others to form anthologies, but they need not necessarily be used or shown in their entirety. All copies of off-air recordings must include the copyright notice on the broadcast program as recorded. These guidelines apply only to nonprofit educational institutions, which are further expected to establish appropriate control procedures to maintain the integrity of these guidelines. Certain public broadcasting services (e.g. Public Broadcasting Service) impose similar restrictions but limit use to only the seven-day period following local broadcast. This broadcast was videotaped, the original was aired on 12/02/11 on the National Scratch Broadcasting Channel (28)
