SMPTE timecode ( or ) is a set of cooperating standards to label individual frames of video or film with a
timecode
A timecode (alternatively, time code) 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 applications which require temporal coordinatio ...
. The system is defined by the
Society of Motion Picture and Television Engineers
The Society of Motion Picture and Television Engineers (SMPTE) (, rarely ), founded in 1916 as the Society of Motion Picture Engineers or SMPE, is a global professional association of engineers, technologists, and executives working in the m ...
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.
Timecodes are added to
film
A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...
,
video
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) syste ...
or audio material, and have also been adapted to synchronize
music
Music is generally defined as the art of arranging sound to create some combination of form, harmony, melody, rhythm or otherwise expressive content. Exact definitions of music vary considerably around the world, though it is an aspect ...
and
theatrical production
A theatrical production is any work of theatre, such as a staged play, musical, comedy or drama produced from a written book or script. Theatrical productions also extend to other performance designations such as Dramatic and Nondramatic theatre, a ...
. They provide a time reference for editing,
synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
and identification. Timecode is a form of media
metadata
Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive metadata – the descriptive ...
. The invention of timecode made modern
videotape editing Linear video editing is a video editing post-production process of selecting, arranging and modifying images and sound in a predetermined, ordered sequence. Regardless of whether it was captured by a video camera, tapeless camcorder, or recorded in ...
possible and led eventually to the creation of
non-linear editing system
Non-linear editing is a form of offline editing for audio, video, and image editing. In offline editing, the original content is not modified in the course of editing. In non-linear editing, edits are specified and modified by specialized sof ...
s.
Basic concepts
SMPTE timecode is presented in ''hour:minute:second:frame'' format and is typically represented in 32 bits using
binary-coded decimal. There are also ''drop-frame'' and ''color framing'' flags and three extra ''binary group flag'' bits used for defining the use of the user bits. The formats of other varieties of SMPTE timecode are derived from that of the
linear timecode
Linear (or Longitudinal) 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 bi ...
. More complex timecodes such as
vertical interval timecode
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.
With one exception, VITC ...
can also include extra information in a variety of encodings.
Sub-second timecode time values are expressed in terms of frames. Common supported
frame rate
Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images (frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be ca ...
s include:
* 24 frame/sec (
film
A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...
,
ATSC, 2K,
4K, 6K)
* 25 frame/sec (
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
(Europe, Uruguay, Argentina, Australia),
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
,
DVB
Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...
, ATSC)
* 29.97 (30 ÷ 1.001) frame/sec (
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
American System (US, Canada, Mexico, Colombia, etc.), ATSC,
PAL-M
PAL-M is the analogue TV system used in Brazil since 19 February 1972. At that time, Brazil was the first South American country to broadcast in colour. Colour TV broadcast began on 19 February 1972, when the TV networks Globo and Bandeirantes t ...
(Brazil))
* 30 frame/sec (
ATSC)
In general, SMPTE timecode frame rate information is implicit, known from the rate of arrival of the timecode from the medium. It may also be specified in other metadata encoded in the medium. The interpretation of several bits, including the ''color framing'' and ''drop frame'' bits, depends on the underlying data rate. In particular, the drop frame bit is only valid for 29.97 and 30 frame/s.
Discontinuous timecode, and flywheel processing
Timecodes are generated as a continuous stream of sequential data values. In some applications
wall-clock time Elapsed real time, real time, wall-clock time, wall time, or walltime is the actual time taken from the start of a computer program to the end. In other words, it is the difference between the time at which a task finishes and the time at which the ...
is used, in others the time encoded is a notional time with more arbitrary reference. After making a series of recordings, or after crude editing, recorded timecodes may consist of discontinuous segments.
In general, it is not possible to know the linear timecode (
LTC) of the current frame until the frame has already gone by, by which time it is too late to make an edit. Practical systems watch the ascending sequence of the timecode and infer the time of the current frame from that.
As timecodes in analog systems are prone to bit-errors and drop-outs, most timecode processing devices check for internal consistency in the sequence of timecode values and use simple error correction schemes to correct for short error bursts. Thus, a boundary between discontinuous timecode ranges cannot be determined exactly until several subsequent frames have passed.
Drop-frame timecode
Drop-frame timecode originates from a compromise introduced when color NTSC video was invented. The NTSC designers wanted to retain compatibility with existing monochrome televisions. To minimize subcarrier visibility on a monochrome receiver it was necessary to make the color subcarrier an odd multiple of half the line scan frequency; the multiple originally chosen was 495. With a 30 Hz frame rate the line scan frequency is (30 × 525) = 15750 Hz. So the subcarrier frequency would have been × 15750 = 3.898125 MHz. This was the subcarrier frequency originally chosen, but tests showed that on some monochrome receivers an interference pattern caused by the beat between the color subcarrier and the 4.5 MHz sound intercarrier could be seen. The visibility of this pattern could be greatly reduced by lowering the subcarrier frequency multiple to 455 (thus increasing the beat frequency from approx 600 kHz to approx 920 kHz) and by making the beat frequency also equal to an odd multiple of half the line scan frequency. This latter change could have been achieved by raising the sound intercarrier by 0.1% to 4.5045 MHz, but the designers, concerned that this might cause problems with some existing receivers, decided instead to reduce the color subcarrier frequency, and thus both the line scan frequency and the frame rate, by 0.1% instead. Thus the NTSC color subcarrier ended up as 3.579 MHz ( MHz), the line scan frequency as 15. kHz ( MHz) and the frame rate 29. Hz ( Hz).
The altered frame rate meant that an "hour of timecode" at a nominal frame rate of 29.97 frame/s was longer than an hour of wall-clock time by 3.6 seconds (for 29.97 non-drop timecode of 01:00:00:00 drop-frame timecode is 01:00:03;18 and for non-drop 00:59:56:12 drop-frame is 01:00:00;00), leading to an error of almost a minute and a half over a day.
To correct this, drop-frame SMPTE timecode was invented. In spite of what the name implies, ''no'' video frames are dropped or skipped when using drop-frame timecode. Rather, some of the ''timecodes'' are dropped. In order to make an hour of timecode match an hour on the clock, drop-frame timecode skips frame numbers 0 and 1 of the first second of every minute, except when the number of minutes is divisible by ten. This causes timecode to skip 18 frames each ten minutes (18,000 frames @ 30 frame/s) and almost perfectly compensates for the difference in rate (but still accumulates 1 frame every 9 hours 15 minutes).
For example, the sequence when frame counts are dropped:
:01:08:59:28
:01:08:59:29
:01:09:00:02
:01:09:00:03
For each tenth minute
:01:09:59:28
:01:09:59:29
:01:10:00:00
:01:10:00:01
While non-drop timecode is displayed with colons separating the digit pairs—"HH:MM:SS:FF"—drop-frame is usually represented with a semicolon (;) or period (.) as the divider between all the digit pairs—"HH;MM;SS;FF", "HH.MM.SS.FF"—or just between the seconds and frames—"HH:MM:SS;FF" or "HH:MM:SS.FF". Drop-frame timecode is typically abbreviated as DF and non-drop as NDF.
Color framing and timecode
A
color framing
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 ...
bit is often used to indicate field 1 of the color frame so that editing equipment can make sure to edit only on appropriate color frame sequence boundaries in order to prevent picture corruption.
Studio operations and master clocks
In
television studio
A television studio, also called a television production studio, is an installation room in which video productions take place, either for the production of live television and its recording onto video tape or other media such as SSDs, or for ...
operations, longitudinal timecode is generated by the studio
master sync generator A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric m ...
and distributed from a central point. Central sync generators usually derive their timing from an
atomic clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
, using either network time or
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
. Studios usually operate multiple clocks and automatically switch over if one fails.
Music production
Longitudinal SMPTE timecode is widely used to synchronize music. A frame rate of 30 frame/s is often used for audio in America, Japan, and other countries that rely on a 60 Hz mains frequency and use the
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
television standard. The
European Broadcasting Union
The European Broadcasting Union (EBU; french: Union européenne de radio-télévision, links=no, UER) is an alliance of Public broadcasting, public service media organisations whose countries are within the European Broadcasting Area or who ar ...
standard frame rate of 25 frame/s is used throughout Europe, Australia and wherever the mains frequency is 50 Hz and the
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
or
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
television standards are used.
Variants
Timecode may be attached to a recording medium in a number of different ways.
#
Linear timecode
Linear (or Longitudinal) 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 bi ...
, a.k.a. "longitudinal timecode" and "LTC": suitable to be recorded on an audio channel, or carried by audio wires for distribution within a studio to synchronize recorders and cameras. To read LTC, the recording must be moving, meaning that LTC is useless when the recording is stationary or nearly stationary. This shortcoming led to the development of VITC.
#
Vertical interval timecode
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.
With one exception, VITC ...
, (VITC, pronounced "vit-see"): recorded into the
vertical blanking interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...
of the video signal on each frame of video. The advantage of VITC is that, since it is a part of the playback video, it can be read when the tape is stationary.
#
AES-EBU embedded timecode
AES3 is a standard for the exchange of digital audio signals between professional audio devices. An AES3 signal can carry two channels of pulse-code-modulated digital audio over several transmission media including balanced lines, unbalanced ...
, SMPTE timecode embedded in an AES3 digital audio connection.
#
control track longitudinal timecode
Control track longitudinal timecode, or CTL timecode, developed by JVC in the early 1990s, is a unique technique for embedding, or ''striping'', reference SMPTE timecode onto a videotape.
Similar to the way VITC timecode is embedded in the verti ...
(CTL timecode): SMPTE timecode embedded in the control track of a video tape.
#Visible time code, a.k.a.
burnt-in timecode
Burnt-in timecode (often abbreviated to BITC by analogy to VITC) 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-re ...
and BITC (pronounced "bit-see") - the numbers are burnt into the video image so that humans can easily read the time code. Videotapes that are duplicated with these time code numbers "burnt-in" to the video are known as ''window dubs''.
#Film labels, such as
Keykode.
History
Timecode was developed in 1967 by EECO,
an electronics company that developed video recorders, and later video production systems. EECO assigned its intellectual property to permit public use.
See also
*
Burnt-in timecode
Burnt-in timecode (often abbreviated to BITC by analogy to VITC) 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-re ...
*
Field dominance In video engineering, field dominance refers to the choice of which field of an interlaced video signal is chosen as the point at which video edits or switches occur.
There are two main choices for field dominance: odd or even. With odd field domi ...
*
IRIG timecode
Inter-range instrumentation group timecodes, commonly known as IRIG timecode, are standard formats for transferring timing information. Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG outp ...
*
Linear timecode
Linear (or Longitudinal) 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 bi ...
*
MIDI timecode
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 ...
*
Rewritable consumer timecode The Rewriteable Consumer Timecode (RCTC, RC Timecode, or RC Time Code) is a nearly frame accurate timecode method developed by Sony for 8mm and Hi8 analog tape formats.
*
Vertical interval timecode
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.
With one exception, VITC ...
Notes
References
*
*
External links
Technical Introduction to Timecodeby Charles Poynton
*
with c source code by Brooks Harris
{{SMPTE standards
Encodings
Timecodes
SMPTE standards