Vertical Interval Timecode (VITC, pronounced "vitsee") is a form of SMPTE timecode encoded on one scan line in a video signal. These lines are typically inserted into the vertical blanking interval of the video signal.
SMPTE timecode is a set of cooperating standards to label individual frames of video or film with a timecode. The system is defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification. SMPTE revised the standard in 2008, turning it into a two-part document: SMPTE 12M-1 and SMPTE 12M-2, including new explanations and clarifications.
In a raster graphics display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final line of a frame or field and the beginning of the first line of the next frame. It is present in analog television, VGA, DVI and other signals. During the VBI, the incoming data stream is not displayed on the screen. In raster cathode ray tube displays, the beam is blanked to avoid displaying the retrace line; see raster scan for details. The signal source, such as a television broadcast, does not supply image information during the blanking period.
With one exception, VITC contains the same payload as SMPTE linear timecode (LTC), embedded in a new frame structure with extra synchronization bits and an error-detection checksum. The exception is that VITC is encoded twice per interlaced video frame, once in each field, and one additional bit (the "field flag") is used to distinguish the two fields.
Linear Timecode (LTC) is an encoding of SMPTE timecode data in an audio signal, as defined in SMPTE 12M specification. The audio signal is commonly recorded on a VTR track or other storage media. The bits are encoded using the biphase mark code : a 0 bit has a single transition at the start of the bit period. A 1 bit has two transitions, at the beginning and middle of the period. This encoding is self-clocking. Each frame is terminated by a 'sync word' which has a special predefined sync relationship with any video or film content.
Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured at two different times. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon.
A video frame may contain more than one VITC code if necessary, recorded on different lines. This is often used in production, where different entities may want to encode different sets of time-code metadata on the same tape.
As a practical matter, VITC can be more 'frame-accurate' than LTC, particularly at very slow tape speeds on analog formats. LTC readers can lose track of code at slow jog speeds whereas VITC can be read frame-by-frame if need be. Conversely, at high speeds (FF/rew.), the VITC is often unreadable due to image distortions, so the LTC is often used instead. Some VCRs have an auto selection between the two formats to provide the highest accuracy.
VITC is 90 bits long: 32 bits of time code, 32 bits of user data, 18 synchronization bits, and 8 bits of checksum. It is transmitted using non-return-to-zero encoding at a bit rate of 115 times the line rate. (The unused 25 bit times are to leave room for the horizontal blanking interval.)
In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with no other neutral or rest condition. The pulses in NRZ have more energy than a return-to-zero (RZ) code, which also has an additional rest state beside the conditions for ones and zeros. NRZ is not inherently a self-clocking signal, so some additional synchronization technique must be used for avoiding bit slips; examples of such techniques are a run-length-limited constraint and a parallel synchronization signal.
Horizontal blanking interval refers to a part of the process of displaying images on a computer monitor or television screen via raster scanning. CRT screens display images by moving beams of electrons very quickly across the screen. Once the beam of the monitor has reached the edge of the screen, the beam is switched off, and the deflection circuit voltages are returned to the values they had for the other edge of the screen; this would have the effect of retracing the screen in the opposite direction, so the beam is turned off during this time. This part of the line display process is the Horizontal Blank.
| Frame number|
(0–23, 24, or 29)
|80||1||0||CRC bits (g(x) = x8 + 1)|
NTSC, named after the National Television System Committee, is the analog television color system that was used in North America from 1954 and until digital conversion, was used in most of the Americas ; Myanmar; South Korea; Taiwan; Philippines; Japan; and some Pacific island nations and territories.
In video engineering, color framing refers to the color frame sequence of fields in a composite video signal through which the video frame timing and chrominance subcarrier signal timing—in particular, that of the color burst -- cycle through all possible phase relationships.
SECAM, also written SÉCAM, is an analogue color television system first used in France. It was one of three major colour television standards, the others being the European PAL and North American NTSC.
The exact nature of the color frame sequence depends on the video standard being used. In the case of the three main composite video standards, PAL video has an 8-field (4 frame) color frame sequence, and NTSC and SECAM both have 4-field (2 frame) color frame sequences.
Preserving the color framing sequence of video across edits and between channels in video effects was an important issue in early analog composite videotape editing systems, as cuts between different color sequences would cause jumps in subcarrier phase, and mixing two signals of different field dominance would result in color artifacts on the part of the signal that was not in sync with the output color frame sequence.
To help prevent these problems, SMPTE time code contains a color framing bit, which can be used to indicate that the video material the timecode refers to follows a standard convention regarding the synchronization of video time code and the color framing sequence. If the color framing bit was set in both types of material, the editing system could then always ensure that color framing was preserved by constraining edit decisions between input sources to keep the correct relationship between the timecode sequences, and hence the color framing sequences.
Related technologies and standards
Burnt-in timecode is a human-readable on-screen version of the timecode information for a piece of material superimposed on a video image. BITC is sometimes used in conjunction with "real" machine-readable timecode, but more often used in copies of original material on to a non-broadcast format such as VHS, so that the VHS copies can be traced back to their master tape and the original time codes easily located.
Control track longitudinal, or CTL, timecode, developed by JVC in the early 1990s, is a unique technique for embedding, or striping, reference SMPTE timecode onto a videotape.
MIDI time code (MTC) embeds the same timing information as standard SMPTE timecode as a series of small 'quarter-frame' MIDI messages. There is no provision for the user bits in the standard MIDI time code messages, and SysEx messages are used to carry this information instead. The quarter-frame messages are transmitted in a sequence of eight messages, thus a complete timecode value is specified every two frames. If the MIDI data stream is running close to capacity, the MTC data may arrive a little behind schedule which has the effect of introducing a small amount of jitter. In order to avoid this it is ideal to use a completely separate MIDI port for MTC data. Larger full-frame messages, which encapsulate a frame worth of timecode in a single message, are used to locate to a time while timecode is not running.
Analog television or analogue television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by rapid variations of either the amplitude, frequency or phase of the signal.
Standard-definition television is a television system which uses a resolution that is not considered to be either high or enhanced definition. The two common SDTV signal types are 576i, with 576 interlaced lines of resolution, derived from the European-developed PAL and SECAM systems; 480i based on the American NTSC system. SDTV and high-definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions.
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode ray tube (CRT) systems which were later replaced by flat panel displays of several types.
Compact Disc Digital Audio, also known as Audio CD, is the standard format for audio compact discs. The standard is defined in the Red Book, one of a series of "Rainbow Books" that contain the technical specifications for all CD formats.
A timecode is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other application which require temporal coordination or logging of recording or actions.
Telecine is the process of transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process. Telecine enables a motion picture, captured originally on film stock, to be viewed with standard video equipment, such as television sets, video cassette recorders (VCR), DVD, Blu-ray Disc or computers. Initially, this allowed television broadcasters to produce programmes using film, usually 16mm stock, but transmit them in the same format, and quality, as other forms of television production. Furthermore, telecine allows film producers, television producers and film distributors working in the film industry to release their products on video and allows producers to use video production equipment to complete their filmmaking projects. Within the film industry, it is also referred to as a TK, because TC is already used to designate timecode.
Serial digital interface (SDI) is a family of digital video interfaces first standardized by SMPTE in 1989. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.
SMPTE 292 is a digital video transmission standard published by the Society of Motion Picture and Television Engineers (SMPTE) which expands upon SMPTE 259 and SMPTE 344 allowing for bit-rates of 1.485 Gbit/s, and 1.485/1.001 Gbit/s. These bit-rates are sufficient for and often used to transfer uncompressed high-definition video.
Ancillary data, in the context of television systems, refers to a means which by non-video information may be embedded within the serial digital interface. Ancillary data is standardized by SMPTE as SMPTE 291M: Ancillary Data Packet and Space Formatting.
ITU-R Recommendation BT.656, sometimes also called ITU656, describes a simple digital video protocol for streaming uncompressed PAL or NTSC Standard Definition TV signals. The protocol builds upon the 4:2:2 digital video encoding parameters defined in ITU-R Recommendation BT.601, which provides interlaced video data, streaming each field separately, and uses the YCbCr color space and a 13.5 MHz sampling frequency for pixels.
The Rewriteable Consumer Timecode is a nearly frame accurate timecode method developed by Sony for 8mm and Hi8 analog tape formats. The RC timecode is written by the video camera directly to analog tape tracks and records the hour, minute, second and frame for each frame of video recorded to tape. Officially, RCTC is accurate to within ±2 to 5 frames. The RC timecode information is written in a separate area of the track so as to not disturb the audio or video information recorded on the tape. The RC timecode was used in conjunction with the datacode to record date, time and frame information directly to the 8mm tape tracks.
A video decoder is an electronic circuit, often contained within a single integrated circuit chip, that converts base-band analog video signals to digital components video. Video decoders commonly allow programmable control over video characteristics such as hue, contrast, and saturation. A video decoder performs the inverse function of a video encoder, which converts raw (uncompressed) digital video to analog video. Video decoders are commonly used in video capture devices and frame grabbers.
Broadcast-safe video is a term used in the broadcast industry to define video and audio compliant with the technical or regulatory broadcast requirements of the target area or region the feed might be broadcasting to. In the United States, the Federal Communications Commission (FCC) is the regulatory authority; in most of Europe, standards are set by the European Broadcasting Union (EBU).