IEC 60461:2010
(Main)Time and control code
Time and control code
IEC 60461:2012 specifies a digital time and control code for use in television, film, and accompanying audio systems operating at nominal rate of 60, 59, 94, 50, 30, 29, 97, 25, 24 and 23,98 frames per second. This International Standard specifies a time address, binary groups, and flag bit structure. In addition, the standard specifies a binary group flag assignment, a linear time code transport, and a vertical interval time code transport. It cancels and replaces the third edition published in 2001, of which it constitutes a technical revision. It includes the following significant change with regard to the previous edition: The time code for progressive television systems with a frame rate greater than 30 frames per second is added. This bilingual version (2012-01) corresponds to the monolingual English version, published in 2010-03.
Code temporel et de commande
La IEC 60461 :2010 spécifie un code temporel et de commande numérique destiné aux systèmes de télévision, films et systèmes audio annexes, fonctionnant à des fréquences image nominales de 60, 59,94, 50, 30, 29,97, 25, 24 et 23,98 images par seconde. La présente Norme internationale spécifie une structure d'adresse temporelle, de groupes binaires et de bits drapeaux. Cette norme spécifie en outre une affectation des drapeaux des groupes binaires, un transport linéaire du code temporel et un transport du code temporel dans l'intervalle vertical. Cette quatrième édition annule et remplace la troisième édition parue en 2001, dont elle constitue une révision technique. Par rapport à l'édition précédente elle comporte la modification significative suivante: est ajouté le code temporel pour des systèmes de télévision à balayage progressif de fréquence image supérieure à 30 images par seconde. La présente version bilingue (2012-02) correspond à la version anglaise monolingue publiée en 2010-03.
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Standards Content (Sample)
IEC 60461 ®
Edition 4.0 2010-03
INTERNATIONAL
STANDARD
Time and control code
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IEC 60461 ®
Edition 4.0 2010-03
INTERNATIONAL
STANDARD
Time and control code
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 33.160.40; 33.170 ISBN 978-2-88910-197-9
– 2 – 60461 © IEC:2010(E)
CONTENTS
FOREWORD.6
INTRODUCTION.8
1 Scope.9
2 Normative references.9
3 Terms, definitions and reserved .9
3.1 Terms and definitions .9
3.2 Reserved.11
4 Time representation in 30 frames per second and 60 frames per second systems .11
4.1 Definitions of real time and NTSC time.11
4.1.1 Definition of real time.11
4.1.2 Definition of NTSC time .11
4.2 Time address of a frame.11
4.2.1 Definition of time address of a frame.11
4.2.2 Non-drop frame – Uncompensated mode .12
4.2.3 Drop frame – NTSC time compensated mode.12
4.3 Colour frame identification in NTSC analogue composite television systems.12
5 Time representation in 25 frames per second and 50 frames per second systems .12
5.1 Definition of real time.12
5.2 Time address of a frame.12
5.3 Colour frame identification in PAL analogue composite television systems .13
5.3.1 Colour frame identification .13
5.3.2 Logical relationship .13
5.3.3 Arithmetic relationship .13
6 Time representation in 24-frame systems.13
6.1 Definitions of real time and NTSC time.13
6.1.1 Definition of real time.13
6.1.2 Definition of NTSC time .14
6.2 Time address of a frame.14
7 Structure of the time address and control bits.14
7.1 Numeric code .14
7.2 Time address .14
7.3 Flag bits .14
7.3.1 Definition of flag bits .14
7.3.2 Drop frame flag (NTSC composite television system only) .14
7.3.3 Colour frame flag (NTSC and PAL composite television systems only).14
7.3.4 Binary group flags.15
7.3.5 Modulation method specific flag .15
7.4 Use of the binary groups.15
7.4.1 Binary group flag assignments .15
7.4.2 Character set not specified and unspecified clock time (BGF2=0,
BGF1=0, BGF0=0) .15
7.4.3 Eight-bit character set and unspecified clock time (BGF2=0, BGF1=0,
BGF0=1).15
7.4.4 Date/time zone and unspecified clock time (BGF2=1, BGF1=0,
BGF0=0).16
7.4.5 Page/line multiplex system and unspecified clock time (BGF2=1,
BGF1=0, BGF0=1) .16
60461 © IEC:2010(E) – 3 –
7.4.6 Clock time specified and unspecified character set (BGF2=0, BGF1=1,
BGF0=0).16
7.4.7 Unassigned binary group usage and unassigned clock time (BGF2=0,
BGF1=1, BGF0=1) .16
7.4.8 Date/time zone and clock time (BGF2=1, BGF1=1, BGF0=0) .16
7.4.9 Specified clock time and page/line multiplex system (BGF2=1,
BGF1=1, BGF0=1) .16
7.5 Clock time reference – Binary group flag combinations.16
8 Linear time code application.17
8.1 Code word format .17
8.2 Code word data content .17
8.2.1 LTC code word content .17
8.2.2 Time address.17
8.2.3 Flag bits .17
8.2.4 Binary groups .18
8.2.5 Synchronization word .18
8.2.6 Biphase mark polarity correction .19
8.3 Modulation method .19
8.4 Bit rate .20
8.5 Timing of the code word relative to a television signal .20
8.6 Linear time code interface electrical and mechanical characteristics.21
8.6.1 Measurements .21
8.6.2 Rise/fall time.21
8.6.3 Amplitude distortion .21
8.6.4 Timing of the transitions.21
8.6.5 Interface connector .21
8.6.6 Output impedance.21
8.6.7 Output amplitude .21
9 Vertical interval application – Analogue television systems .26
9.1 Code word format .26
9.2 Code word data content .26
9.2.1 VITC code word content.26
9.2.2 Time address.29
9.2.3 Flag bits .29
9.2.4 Binary groups .29
9.2.5 Field mark flag.30
9.2.6 Synchronization bits.30
9.2.7 Cyclic redundance check code .30
9.3 Modulation method .31
9.4 Bit timing .31
9.5 Timing of the code word relative to the television signal .32
9.5.1 525/59,94 television system .32
9.5.2 625/50 television system .32
9.6 Location of the address code signal in the vertical interval .32
9.6.1 Location of the VITC code.32
9.6.2 525/59,94 television system .32
9.6.3 625/50 television system .32
9.6.4 Component television system.32
9.7 Redundancy .32
– 4 – 60461 © IEC:2010(E)
9.8 Vertical interval time code waveform characteristics.33
9.8.1 Waveform characteristics.33
9.8.2 Logic level .33
9.8.3 Rise/fall time.33
9.8.4 Amplitude distortion .33
10 Relationship between LTC and VITC .33
10.1 Time address data.33
10.2 Binary group data .33
10.2.1 General .33
10.2.2 Transferring vertical interval binary group data to linear binary group
data.34
10.2.3 Transferring linear binary group data to vertical interval binary group
data.34
10.3 VITC and LTC code word comparison .34
11 Progressive systems with frame rates greater than 30 frames per second .36
11.1 Time address of a frame pair in 50 and 60 frames per second progressive
systems.36
11.2 Implementation guidelines .36
Annex A (informative) Explanatory notes .37
Annex B (informative) Converting time codes when converting video from 24 fps
television systems.39
Bibliography .42
Figure 1 – Linear time code source output waveform .20
Figure 2 – 29,97/30 frame linear time code example.22
Figure 3 – 25 frame linear time code example .23
Figure 4 – 24 frame linear time code example .24
Figure 5 – Linear time code relationship to 59,94 frame progressive video example .25
Figure 6 – 525/59,94 vertical interval time code address bit assignment and timing.27
Figure 7 – 625/50 vertical interval time code address bit assignment and timing .28
Figure 8 – Vertical interval time code waveform .31
Figure 9 – Example of frame labeling for 50 and 60 frames per second progressive
systems .36
Figure B.1 – Example of conversion of 23,98 fps video to 525/59,94/I .40
Figure B.2 – Example of conversion of 24 fps high definition video to 625/50/I .41
Table 1 – Binary group flag assignments .15
Table 2 – LTC time address bit positions .17
Table 3 – LTC flag bit positions .18
Table 4 – LTC binary group bit positions.18
Table 5 – LTC synchronization word bit positions and values .19
Table 6 – VITC time address bit positions.29
Table 7 – VITC flag bit positions.29
Table 8 – VITC binary group bit positions .30
Table 9 – CRC bit positions.31
Table 10 – VITC logic level ranges .33
60461 © IEC:2010(E) – 5 –
Table 11 – Summation of VITC and LTC codeword bit definitions .35
– 6 – 60461 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TIME AND CONTROL CODE
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60461 has been prepared by technical area 6: Professional
electronics storage media, data structures and equipment, of IEC technical committee 100:
Audio, video and multimedia systems and equipment.
This fourth edition cancels and replaces the third edition published in 2001, of which it
constitutes a technical revision.
It includes the following significant change with regard to the previous edition: The time code
for progressive television systems with a frame rate greater than 30 frames per second is
added.
The text of this standard is based on the following documents:
CDV Report on voting
100/1515/CDV 100/1616/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
60461 © IEC:2010(E) – 7 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
– 8 – 60461 © IEC:2010(E)
INTRODUCTION
IEC 60461 was originally developed for analogue television recording systems and thus dealt
only with interlaced television systems operating with frame rates up to 30 frames per second.
It is, however, flexible enough in design to be used in digital television systems, both standard
definition and high definition. The support for progressive video systems with frame rates
above 30 frames per second is described in this International Standard.
Clauses 4, 5, and 6 specify the manner in which time is represented in frame-based systems.
Clause 7 specifies the structure of the time address and control bits of the code, and sets
guidelines for storage of user data in the code. Clause 8 specifies the modulation method and
interface characteristics of a linear time code (LTC) source. Clause 9 specifies the modulation
method for inserting the code into the vertical interval of a television signal. Clause 10
summarises the relationship between the two forms of time and control code. Clause 11
summarises time code implementations for video formats with frame rates greater than 30 fps.
60461 © IEC:2010(E) – 9 –
TIME AND CONTROL CODE
1 Scope
This International Standard specifies a digital time and control code for use in television, film,
and accompanying audio systems operating at nominal rate of 60, 59,94, 50, 30, 29,97, 25, 24
and 23,98 frames per second. This International Standard specifies a time address, binary
groups, and flag bit structure. In addition, the standard specifies a binary group flag
assignment, a linear time code transport, and a vertical interval time code transport.
This International Standard defines primary data transport structures for linear time code (LTC)
and vertical interval time code (VITC). This standard specifies the LTC modulation and timing
for all video formats. This standard also defines the VITC modulation and location for
525/59,94 and 625/50 analogue composite and component systems only.
NOTE The digital representation of analogue VITC (D-VITC) is specified in SMPTE 266M and is defined for
525/59,94 and 625/50 digital component systems only. High definition formats, such as those documented in
SMPTE 274M and SMPTE 296M, should use ancillary time code (ATC) as specified in SMPTE 12M-2 (formerly
SMPTE RP 188) for transport of time code in the digital video data stream. For future implementations of time code
for digital standard definition formats, the use of ATC rather than D-VITC is encouraged.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
ISO/IEC 646:1991, Information processing – ISO 7-bit coded character set for information
interchange
ISO/IEC 2022:1994, Information technology – Character code structure and extension
techniques
ITU-R BT.1700-1(2005), Annex 2, Characteristics of composite video signals for conventional
analogue television systems
SMPTE 170M:2004, Television – Composite Analog Video Signal – NTSC for Studio
Applications
SMPTE 258M:1993, Television – Transfer of Edit Decision Lists
SMPTE 262M:1995, Television, Audio and Film – Binary Groups of Time and Control Codes –
Storage and Transmission of Data
SMPTE 309M:1999, Television – Transmission of Date and Time Zone Information in Binary
Groups of Time and Control Code
3 Terms, definitions and reserved
3.1 Terms and definitions
For the purposes of this document the following terms and definitions apply.
– 10 – 60461 © IEC:2010(E)
3.1.1
binary coded decimal system
BCD system
means for encoding decimal numbers as groups of binary bits
NOTE 1 Each decimal digit (0-9) is represented by a unique four-bit code. The four bits are weighted with the
digit's decimal weight multiplied by successive powers of two.
0 1 2 3
NOTE 2 For example, the bit weights for a "units" digit would be 1 × 2 , 1 × 2 , 1 × 2 , and 1 × 2 , while the bit
0 1 2 3
weights for a "tens" digit would be 10 × 2 , 10 × 2 , 10 × 2 , and 10 × 2 .
3.1.2
frame
contains all of the lines of spatial information of a video signal required to make up one
complete picture (including any necessary associated synchronization lines)
NOTE For progressive video, these lines contain picture samples, captured at one time instant, starting from the
top of the frame and continuing through successive lines to the bottom of the frame.
3.1.3
field
frame consists of two fields for interlaced video: one of these fields will commence one field
period later than the other
NOTE See SMPTE 170M for an example of such a system. Composite television standards might require multiple
fields in a “colour sequence,” but that does not alter this standard’s nominal terminology.
3.1.4
linear time code
LTC
code word format and modulation system which is normally used to record the time code signal
on a linear recording medium or to transport the serial signal over an interface independent of
any video signal
3.1.5
vertical interval time code
VITC
code word format and modulation system used to insert the time code signal in an active line
within the vertical blanking interval of an analogue standard definition television (SDTV) signal
3.1.6
time and control code
encompasses all aspects of the time address, flag bits, and binary groups for user-defined data
codes, as well as two methods of modulation of the resulting code words
NOTE It is commonly abbreviated as “time code” (note also that some users spell this “timecode”).
3.1.7
time code source
any device which generates a time and control code signal, or regenerates a time and control
code signal from a recorded medium or transmission channel
3.1.8
original source
refers specifically to a device which is generating the time and control code signal in
synchronization with its associated video and/or audio
NOTE The time address and binary group (“user data”) payload is attached to a particular frame or frame pairs
either directly or by reference within the user’s system. For frame-based systems the time address that forms part
of the time code is primarily intended as a label to identify discrete frames. It also may imply that a particular frame
60461 © IEC:2010(E) – 11 –
has had, has now, or will have, a temporal relationship to something else, such as the frame's position in a
sequence of frames or synchronization to a reference signal.
3.2 Reserved
Indicates a provision that it is not defined at this time, shall not be used, and may be defined in
future.
4 Time representation in 30 frames per second and 60 frames per second
systems
4.1 Definitions of real time and NTSC time
4.1.1 Definition of real time
In a system running at a frame rate of 30 frames per second (fps), exactly one second of real
time elapses during the scanning of 30 frames. In a system operating at a frame rate of 60 fps,
exactly one second of real time elapses during the duration of 60 frames.
4.1.2 Definition of NTSC time
In an NTSC television system operating at a vertical field rate of 60/1,001 fields per second
(≈59,94 Hz), one second of NTSC time elapses during the scanning of 60 television fields or 30
television frames. Because of the difference in vertical scanning rates, the relationship
between real time and NTSC time is
1 s = 1,001 s
NTSC REAL
NOTE 1 There are other television systems (such as some HDTV systems) which operate at 24/1,001, 30/1,001,
or 60/1,001 frames per second. The term “NTSC time” is used to indicate its historical origins and to describe the
common frame time base of all of these systems.
NOTE 2 The results of dividing the integer frame rates by 1,001 do not result in precise decimal numbers, for
example, 30/1,001 is 29,970 029 970 029. (to 12 decimals). This is commonly abbreviated as 29,97. In a similar
manner, it is common to abbreviate 24/1,001 as 23,98, and 60/1,001 as 59,94. These abbreviations are used
throughout this standard. Sufficient precision is necessary in calculations to assure that rounding or truncation
operations will not create errors in the end result. This is particularly important when calculating audio sample
alignments or when long-term time keeping is required.
4.2 Time address of a frame
4.2.1 Definition of time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. For systems operating at 60 frames per second, each frame pair
shall be identified by a unique and complete address consisting of an hour, minute, second,
and frame number. Refer to SMPTE 258M for standard formats used to display frame-based
time.
The hours, minutes, and seconds follow the ascending progression of a 24-hour clock
beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes, and 59 seconds.
The frames shall be numbered successively according to the counting mode (drop frame or
non-drop frame) as described below:
NOTE See Clause 11 for additional information regarding television systems which operate at 60 frames per
second.
– 12 – 60461 © IEC:2010(E)
4.2.2 Non-drop frame – Uncompensated mode
Frames shall be numbered 0 through 29, successively, with no omissions.
4.2.3 Drop frame – NTSC time compensated mode
Because the vertical field rate of an NTSC television signal is 60/1,001 fields per second
(≈59,94 Hz), straightforward counting at 30 frames per second will yield an error of
approximately +108 frames (+3,6 s) in one hour of running time.
REAL
To minimize the NTSC time error, the first two frame numbers (00 and 01) shall be omitted
from the count at the start of each minute except minutes 00, 10, 20, 30, 40, and 50.
Because the frame rate of a progressive NTSC-time related 60 frames per second television
signal is actually 60/1,001 frames per second, and each time code count references a frame
pair, the same counting mechanism may be applied as well. See Clause 11 for additional
information on this subject.
When drop-frame compensation is applied to an NTSC television time code, the total error
accumulated after one hour is reduced to –3,6 ms. The total error accumulated over a 24-hour
period is –86 ms.
4.3 Colour frame identification in NTSC analogue composite television systems
If colour frame identification in the time code is required, the even units of frame numbers shall
identify colour fields I and II, and the odd units of frame numbers shall identify colour fields III
and IV.
NOTE Even though a component system does not have a colour sequence, the time code may carry colour
sequence information from an original video source so that recoding of a composite signal into a component signal
and back can preserve the original colour sequence relationship.
5 Time representation in 25 frames per second and 50 frames per second
systems
5.1 Definition of real time
In a system running at a frame rate of 25 frames per second, exactly one second of real time
elapses during the scanning of 25 frames. An example of such a system is a 625/50 television
system. In a system running at a frame rate of 50 frames per second, exactly one second of
real time elapses during the duration of 50 frames.
5.2 Time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. For systems operating at 50 frames per second, each frame pair
shall be identified by a unique and complete address consisting of an hour, minute, second,
and frame number.
The hours, minutes, and seconds follow the ascending progression of a 24-hour clock
beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes, and 59 seconds.
The frames (or frame pairs for 50 frames per second systems) shall be numbered successively
0 through 24.
There is no counting mode such as drop frame (which is applicable only to 30 frame counting)
that is applicable to 25 frame counting.
60461 © IEC:2010(E) – 13 –
NOTE See Clause 11 for additional information regarding television systems which operate at frame rates of 50
frames per second.
5.3 Colour frame identification in PAL analogue composite television systems
5.3.1 Colour frame identification
If identification of the eight-field colour sequence in the time code is required, the time address
shall bear a predictable relationship with the eight-field colour sequence (as specified in ITU-R
BT.1700). This relationship can be expressed using either logical or arithmetic notations as
5.3.2 and 5.3.3, r es pec tively.
given in
5.3.2 Logical relationship
Given that the frame and second numbers of the time address are expressed as BCD digit
pairs, the value of the logical expression (A|B) ^ C ^ D ^ E ^ F shall be:
"1" for fields 1, 2, 3, and 4;
"0" for fields 5, 6, 7, and 8
where
A equals the value of the 1's bit of the frame number;
B equals the value of the 1's bit of the second number;
C equals the value of the 2's bit of the frame number;
D equals the value of the 10's bit of the frame number;
E equals the value of the 2's bit of the second number;
F equals the value of the 10's bit of the second number;
| represents the logical OR operation;
^ represents the logical EXCLUSIVE OR operation.
5.3.3 Arithmetic relationship
The remainder of the quotient:
(S +P)
shall be
0 for fields 7 and 8;
1 for fields 1 and 2;
2 for fields 3 and 4;
3 for fields 5 and 6
where
S equals the decimal value of the "seconds" digits of the time address, and
P equals the decimal value of the frames digits of the time address.
6 Time representation in 24-frame systems
6.1 Definitions of real time and NTSC time
6.1.1 Definition of real time
In a system running at a frame rate of 24 frames per second, exactly one second of real time
elapses during the passing of 24 frames. An example of such a system is a film system.
– 14 – 60461 © IEC:2010(E)
6.1.2 Definition of NTSC time
In a NTSC-time related television signal operating at 24/1,001 frames per second
(approximately 23,976), straightforward counting at 24 frames per second will yield a deviation
of approximately 86 frames (3,6 s) in one hour of elapsed time.
Where it is desired to maintain a correspondence with 30 frame per second systems the 30
non-drop frame count mode should be used. For additional details refer to Annex B.1.
6.2 Time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. The hours, minutes, and seconds follow the ascending progression
of a 24 hour clock beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes,
and 59 seconds. The frames shall be numbered successively 0 through 23.
There is no counting mode such as drop frame (which is applicable only to 30 frame counting)
that is applicable to 24 frame counting.
7 Structure of the time address and control bits
7.1 Numeric code
The numeric code consists of sixteen four-bit groups, eight groups containing time address and
flag bits, and eight four-bit binary groups for user-defined data and control codes.
7.2 Time address
The basic structure of the time address is based upon the BCD system, using units and tens in
digit pairs for hours, minutes, seconds, and frames. Some of the digits are limited to values
that do not require all four bits to be significant. These bits are omitted from the time address
and include the "80s" and "40s" of hours, "80s" of minutes, "80s" of seconds, and the "80s" and
"40s" of frames. Thus the entire time address is coded into 26 bits.
7.3 Flag bits
7.3.1 Definition of flag bits
Six bits are reserved for the storage of flags which define the operational mode of the time and
control code. A device which decodes a time and control code may utilize these flags to
interpret properly the time address and binary group data.
7.3.2 Drop frame flag (NTSC composite television system only)
This flag shall be set to 1 when drop frame compensation is being performed as specified in
4.2.3. When the count is not drop frame compensated, this flag bit shall be set to 0.
7.3.3 Colour frame flag (NTSC and PAL composite television systems only)
If colour frame identification has intentionally been applied to the time and control code by the
original source, as defined in 4.3 or 5.3, this flag shall be set to 1. If this flag is set to logical
zero then there is no implied relationship between the colour frame sequence and the time
address.
NOTE Colour frame identification may be forced by an original source of time and control code by halting the time
address until the colour field to time code relationship is satisfied, after which the time address is incremented
normally each frame. As long as neither the time address counting sequence nor the colour field sequence is
changed, the relationship will remain satisfied.
60461 © IEC:2010(E) – 15 –
7.3.4 Binary group flags
Three flags provide eight unique combinations which specify the use of the binary groups (see
7.4). Three combinations of these flags also specify the time address reference as an external
precision clock time reference (see 7.5) and these also select subsets of the binary group
applications.
NOTE The term binary group flags represents its historical origins, however these flags now also signal time
address count parameters.
7.3.5 Modulation method specific flag
The remaining flag bit is reserved for use by each modulation method. This flag is defined in
8.2.6 and 9.2.5.
7.4 Use of the binary groups
7.4.1 Binary group flag assignments
The binary groups are intended for storage and transmission of data by the users. The format
of the data contained in the binary groups is specified by the value of three binary group flag
bits BGF2, BGF1, and BGF0. The following subclauses define the current assignments of the
binary group flag states. Table 1 summarises the present assigned combinations.
NOTE The binary groups are commonly referred to as "user bits"
Table 1 – Binary group flag assignments
BGF2 BGF1 BGF0 Time address Binary group Reference
0 0 0 Unspecified Unspecified 7. 4. 2
0 0 1 Unspecified 8-bit codes 7. 4. 3
1 0 0 Unspecified Date and time zone 7. 4. 4
1 0 1 Unspecified Page/line 7. 4. 5
0 1 0 Clock time Unspecified 7. 4. 6, 7. 5
0 1 1 Unassigned Reserved 7. 4. 7
1 1 0 Clock time Date and time zone 7. 4. 8, 7. 5
1 1 1 Clock time Page/line 7. 4. 9, 7. 5
7.4.2 Character set not specified and unspecified clock time
(BGF2=0, BGF1=0, BGF0=0)
This combination of binary group flags signifies that the time address is not referenced to an
external clock and that the binary groups contain an unspecified character set. If the character
set used for the data insertion is unspecified, the 32 bits within the eight binary groups may be
assigned in any manner without restriction.
7.4.3 Eight-bit character set and unspecified clock time
(BGF2=0, BGF1=0, BGF0=1)
This combination signifies that the time address is not referenced to an external clock and that
the binary groups contain an eight-bit character set conforming to ISO/IEC 646 or
ISO/IEC 2022. If the seven-bit ISO codes are being used, they shall be converted to eight-bit
codes by setting the eighth bit to 0.
– 16 – 60461 © IEC:2010(E)
Four ISO codes may be encoded in the binary groups, each occupying two binary groups. The
first ISO code is contained in binary groups 7 and 8, with the least significant four bits in binary
group 7 and the most significant four bits in binary group 8. The three remaining ISO codes are
stored in binary groups 5/6, 3/4, and 1/2 accordingly.
7.4.4 Date/time zone and unspecified clock time (BGF2=1, BGF1=0, BGF0=0)
This combination signifies that the time address is not referenced to an external clock and that
the binary groups contain date and time zone encoding as described in SMPTE 309M.
7.4.5 Page/line multiplex system and unspecified clock time
(BGF2=1, BGF1=0, BGF0=1)
This combination signifies that the time address is not referenced to an external clock and that
the binary groups contain information formatted according to the page/line multiplex system
described in SMPTE 262M. This multiplex system defines a hierarchy that can be used to
encode large amounts of data in the binary groups through the use of time multiplexing.
Applications for this encoding scheme include control codes, text data, and production
information.
7.4.6 Clock time specified and unspecified character set
(BGF2=0, BGF1=1, BGF0=0)
This combination specifies that the time address is referenced to an external clock and
signifies an unspecified character set.
...
IEC 60461 ®
Edition 4.0 2010-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Time and control code
Code temporel et de commande
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IEC 60461 ®
Edition 4.0 2010-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Time and control code
Code temporel et de commande
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 33.160.40; 33.170 ISBN 978-2-88912-849-5
– 2 – 60461 IEC:2010
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references. 9
3 Terms, definitions and reserved . 9
3.1 Terms and definitions . 9
3.2 Reserved . 11
4 Time representation in 30 frames per second and 60 frames per second systems . 11
4.1 Definitions of real time and NTSC time . 11
4.1.1 Definition of real time . 11
4.1.2 Definition of NTSC time . 11
4.2 Time address of a frame . 11
4.2.1 Definition of time address of a frame . 11
4.2.2 Non-drop frame – Uncompensated mode . 12
4.2.3 Drop frame – NTSC time compensated mode . 12
4.3 Colour frame identification in NTSC analogue composite television systems . 12
5 Time representation in 25 frames per second and 50 frames per second systems . 12
5.1 Definition of real time . 12
5.2 Time address of a frame . 12
5.3 Colour frame identification in PAL analogue composite television systems . 13
5.3.1 Colour frame identification . 13
5.3.2 Logical relationship . 13
5.3.3 Arithmetic relationship . 13
6 Time representation in 24-frame systems . 13
6.1 Definitions of real time and NTSC time . 13
6.1.1 Definition of real time . 13
6.1.2 Definition of NTSC time . 14
6.2 Time address of a frame . 14
7 Structure of the time address and control bits . 14
7.1 Numeric code . 14
7.2 Time address . 14
7.3 Flag bits . 14
7.3.1 Definition of flag bits . 14
7.3.2 Drop frame flag (NTSC composite television system only) . 14
7.3.3 Colour frame flag (NTSC and PAL composite television systems only) . 14
7.3.4 Binary group flags . 15
7.3.5 Modulation method specific flag . 15
7.4 Use of the binary groups . 15
7.4.1 Binary group flag assignments . 15
7.4.2 Character set not specified and unspecified clock time (BGF2=0,
BGF1=0, BGF0=0) . 15
7.4.3 Eight-bit character set and unspecified clock time (BGF2=0, BGF1=0,
BGF0=1) . 15
7.4.4 Date/time zone and unspecified clock time (BGF2=1, BGF1=0,
BGF0=0) . 16
7.4.5 Page/line multiplex system and unspecified clock time (BGF2=1,
BGF1=0, BGF0=1) . 16
60461 IEC:2010 – 3 –
7.4.6 Clock time specified and unspecified character set (BGF2=0, BGF1=1,
BGF0=0) . 16
7.4.7 Unassigned binary group usage and unassigned clock time (BGF2=0,
BGF1=1, BGF0=1) . 16
7.4.8 Date/time zone and clock time (BGF2=1, BGF1=1, BGF0=0) . 16
7.4.9 Specified clock time and page/line multiplex system (BGF2=1,
BGF1=1, BGF0=1) . 16
7.5 Clock time reference – Binary group flag combinations. 16
8 Linear time code application. 17
8.1 Code word format . 17
8.2 Code word data content . 17
8.2.1 LTC code word content . 17
8.2.2 Time address . 17
8.2.3 Flag bits . 17
8.2.4 Binary groups . 18
8.2.5 Synchronization word . 18
8.2.6 Biphase mark polarity correction . 19
8.3 Modulation method . 19
8.4 Bit rate . 20
8.5 Timing of the code word relative to a television signal . 20
8.6 Linear time code interface electrical and mechanical characteristics . 21
8.6.1 Measurements . 21
8.6.2 Rise/fall time . 21
8.6.3 Amplitude distortion . 21
8.6.4 Timing of the transitions . 21
8.6.5 Interface connector . 21
8.6.6 Output impedance . 21
8.6.7 Output amplitude . 21
9 Vertical interval application – Analogue television systems . 26
9.1 Code word format . 26
9.2 Code word data content . 26
9.2.1 VITC code word content . 26
9.2.2 Time address . 29
9.2.3 Flag bits . 29
9.2.4 Binary groups . 29
9.2.5 Field mark flag . 30
9.2.6 Synchronization bits . 30
9.2.7 Cyclic redundance check code . 30
9.3 Modulation method . 31
9.4 Bit timing . 31
9.5 Timing of the code word relative to the television signal . 32
9.5.1 525/59,94 television system . 32
9.5.2 625/50 television system . 32
9.6 Location of the address code signal in the vertical interval . 32
9.6.1 Location of the VITC code . 32
9.6.2 525/59,94 television system . 32
9.6.3 625/50 television system . 32
9.6.4 Component television system . 32
9.7 Redundancy . 32
– 4 – 60461 IEC:2010
9.8 Vertical interval time code waveform characteristics . 33
9.8.1 Waveform characteristics . 33
9.8.2 Logic level . 33
9.8.3 Rise/fall time . 33
9.8.4 Amplitude distortion . 33
10 Relationship between LTC and VITC . 33
10.1 Time address data . 33
10.2 Binary group data . 33
10.2.1 General . 33
10.2.2 Transferring vertical interval binary group data to linear binary group
data . 34
10.2.3 Transferring linear binary group data to vertical interval binary group
data . 34
10.3 VITC and LTC code word comparison . 34
11 Progressive systems with frame rates greater than 30 frames per second . 36
11.1 Time address of a frame pair in 50 and 60 frames per second progressive
systems . 36
11.2 Implementation guidelines . 36
Annex A (informative) Explanatory notes . 37
Annex B (informative) Converting time codes when converting video from 24 fps
television systems . 39
Bibliography . 42
Figure 1 – Linear time code source output waveform . 20
Figure 2 – 29,97/30 frame linear time code example . 22
Figure 3 – 25 frame linear time code example . 23
Figure 4 – 24 frame linear time code example . 24
Figure 5 – Linear time code relationship to 59,94 frame progressive video example . 25
Figure 6 – 525/59,94 vertical interval time code address bit assignment and timing . 27
Figure 7 – 625/50 vertical interval time code address bit assignment and timing . 28
Figure 8 – Vertical interval time code waveform . 31
Figure 9 – Example of frame labeling for 50 and 60 frames per second progressive
systems . 36
Figure B.1 – Example of conversion of 23,98 fps video to 525/59,94/I . 40
Figure B.2 – Example of conversion of 24 fps high definition video to 625/50/I . 41
Table 1 – Binary group flag assignments . 15
Table 2 – LTC time address bit positions . 17
Table 3 – LTC flag bit positions . 18
Table 4 – LTC binary group bit positions . 18
Table 5 – LTC synchronization word bit positions and values . 19
Table 6 – VITC time address bit positions . 29
Table 7 – VITC flag bit positions . 29
Table 8 – VITC binary group bit positions . 30
Table 9 – CRC bit positions . 31
60461 IEC:2010 – 5 –
Table 10 – VITC logic level ranges . 33
Table 11 – Summation of VITC and LTC codeword bit definitions . 35
– 6 – 60461 IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TIME AND CONTROL CODE
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60461 has been prepared by technical area 6: Professional
electronics storage media, data structures and equipment, of IEC technical committee 100:
Audio, video and multimedia systems and equipment.
This fourth edition cancels and replaces the third edition published in 2001, of which it
constitutes a technical revision.
It includes the following significant change with regard to the previous edition: The time code
for progressive television systems with a frame rate greater than 30 frames per second is
added.
This bilingual version (2012-01) corresponds to the monolingual English version, published in
2010-03.
60461 IEC:2010 – 7 –
The text of this standard is based on the following documents:
CDV Report on voting
100/1515/CDV 100/1616/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 8 – 60461 IEC:2010
INTRODUCTION
IEC 60461 was originally developed for analogue television recording systems and thus dealt
only with interlaced television systems operating with frame rates up to 30 frames per second.
It is, however, flexible enough in design to be used in digital television systems, both standard
definition and high definition. The support for progressive video systems with frame rates
above 30 frames per second is described in this International Standard.
Clauses 4, 5, and 6 specify the manner in which time is represented in frame-based systems.
Clause 7 specifies the structure of the time address and control bits of the code, and sets
guidelines for storage of user data in the code. Clause 8 specifies the modulation method and
interface characteristics of a linear time code (LTC) source. Clause 9 specifies the modulation
method for inserting the code into the vertical interval of a television signal. Clause 10
summarises the relationship between the two forms of time and control code. Clause 11
summarises time code implementations for video formats with frame rates greater than 30 fps.
60461 IEC:2010 – 9 –
TIME AND CONTROL CODE
1 Scope
This International Standard specifies a digital time and control code for use in television, film,
and accompanying audio systems operating at nominal rate of 60, 59,94, 50, 30, 29,97, 25, 24
and 23,98 frames per second. This International Standard specifies a time address, binary
groups, and flag bit structure. In addition, the standard specifies a binary group flag
assignment, a linear time code transport, and a vertical interval time code transport.
This International Standard defines primary data transport structures for linear time code (LTC)
and vertical interval time code (VITC). This standard specifies the LTC modulation and timing
for all video formats. This standard also defines the VITC modulation and location for
525/59,94 and 625/50 analogue composite and component systems only.
NOTE The digital representation of analogue VITC (D-VITC) is specified in SMPTE 266M and is defined for
525/59,94 and 625/50 digital component systems only. High definition formats, such as those documented in
SMPTE 274M and SMPTE 296M, should use ancillary time code (ATC) as specified in SMPTE 12M-2 (formerly
SMPTE RP 188) for transport of time code in the digital video data stream. For future implementations of time code
for digital standard definition formats, the use of ATC rather than D-VITC is encouraged.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
ISO/IEC 646:1991, Information processing – ISO 7-bit coded character set for information
interchange
ISO/IEC 2022:1994, Information technology – Character code structure and extension
techniques
ITU-R BT.1700-1(2005), Annex 2, Characteristics of composite video signals for conventional
analogue television systems
SMPTE 170M:2004, Television – Composite Analog Video Signal – NTSC for Studio
Applications
SMPTE 258M:1993, Television – Transfer of Edit Decision Lists
SMPTE 262M:1995, Television, Audio and Film – Binary Groups of Time and Control Codes –
Storage and Transmission of Data
SMPTE 309M:1999, Television – Transmission of Date and Time Zone Information in Binary
Groups of Time and Control Code
3 Terms, definitions and reserved
3.1 Terms and definitions
For the purposes of this document the following terms and definitions apply.
– 10 – 60461 IEC:2010
3.1.1
binary coded decimal system
BCD system
means for encoding decimal numbers as groups of binary bits
NOTE 1 Each decimal digit (0-9) is represented by a unique four-bit code. The four bits are weighted with the
digit's decimal weight multiplied by successive powers of two.
0 1 2 3
NOTE 2 For example, the bit weights for a "units" digit would be 1 × 2 , 1 × 2 , 1 × 2 , and 1 × 2 , while the bit
0 1 2 3
weights for a "tens" digit would be 10 × 2 , 10 × 2 , 10 × 2 , and 10 × 2 .
3.1.2
frame
contains all of the lines of spatial information of a video signal required to make up one
complete picture (including any necessary associated synchronization lines)
NOTE For progressive video, these lines contain picture samples, captured at one time instant, starting from the
top of the frame and continuing through successive lines to the bottom of the frame.
3.1.3
field
frame consists of two fields for interlaced video: one of these fields will commence one field
period later than the other
NOTE See SMPTE 170M for an example of such a system. Composite television standards might require multiple
fields in a “colour sequence,” but that does not alter this standard’s nominal terminology.
3.1.4
linear time code
LTC
code word format and modulation system which is normally used to record the time code signal
on a linear recording medium or to transport the serial signal over an interface independent of
any video signal
3.1.5
vertical interval time code
VITC
code word format and modulation system used to insert the time code signal in an active line
within the vertical blanking interval of an analogue standard definition television (SDTV) signal
3.1.6
time and control code
encompasses all aspects of the time address, flag bits, and binary groups for user-defined data
codes, as well as two methods of modulation of the resulting code words
NOTE It is commonly abbreviated as “time code” (note also that some users spell this “timecode”).
3.1.7
time code source
any device which generates a time and control code signal, or regenerates a time and control
code signal from a recorded medium or transmission channel
3.1.8
original source
refers specifically to a device which is generating the time and control code signal in
synchronization with its associated video and/or audio
NOTE The time address and binary group (“user data”) payload is attached to a particular frame or frame pairs
either directly or by reference within the user’s system. For frame-based systems the time address that forms part
of the time code is primarily intended as a label to identify discrete frames. It also may imply that a particular frame
60461 IEC:2010 – 11 –
has had, has now, or will have, a temporal relationship to something else, such as the frame's position in a
sequence of frames or synchronization to a reference signal.
3.2 Reserved
Indicates a provision that it is not defined at this time, shall not be used, and may be defined in
future.
4 Time representation in 30 frames per second and 60 frames per second
systems
4.1 Definitions of real time and NTSC time
4.1.1 Definition of real time
In a system running at a frame rate of 30 frames per second (fps), exactly one second of real
time elapses during the scanning of 30 frames. In a system operating at a frame rate of 60 fps,
exactly one second of real time elapses during the duration of 60 frames.
4.1.2 Definition of NTSC time
In an NTSC television system operating at a vertical field rate of 60/1,001 fields per second
(≈59,94 Hz), one second of NTSC time elapses during the scanning of 60 television fields or 30
television frames. Because of the difference in vertical scanning rates, the relationship
between real time and NTSC time is
1 s = 1,001 s
NTSC REAL
NOTE 1 There are other television systems (such as some HDTV systems) which operate at 24/1,001, 30/1,001,
or 60/1,001 frames per second. The term “NTSC time” is used to indicate its historical origins and to describe the
common frame time base of all of these systems.
NOTE 2 The results of dividing the integer frame rates by 1,001 do not result in precise decimal numbers, for
example, 30/1,001 is 29,970 029 970 029. (to 12 decimals). This is commonly abbreviated as 29,97. In a similar
manner, it is common to abbreviate 24/1,001 as 23,98, and 60/1,001 as 59,94. These abbreviations are used
throughout this standard. Sufficient precision is necessary in calculations to assure that rounding or truncation
operations will not create errors in the end result. This is particularly important when calculating audio sample
alignments or when long-term time keeping is required.
4.2 Time address of a frame
4.2.1 Definition of time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. For systems operating at 60 frames per second, each frame pair
shall be identified by a unique and complete address consisting of an hour, minute, second,
and frame number. Refer to SMPTE 258M for standard formats used to display frame-based
time.
The hours, minutes, and seconds follow the ascending progression of a 24-hour clock
beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes, and 59 seconds.
The frames shall be numbered successively according to the counting mode (drop frame or
non-drop frame) as described below:
NOTE See Clause 11 for additional information regarding television systems which operate at 60 frames per
second.
– 12 – 60461 IEC:2010
4.2.2 Non-drop frame – Uncompensated mode
Frames shall be numbered 0 through 29, successively, with no omissions.
4.2.3 Drop frame – NTSC time compensated mode
Because the vertical field rate of an NTSC television signal is 60/1,001 fields per second
(≈59,94 Hz), straightforward counting at 30 frames per second will yield an error of
approximately +108 frames (+3,6 s) in one hour of running time.
REAL
To minimize the NTSC time error, the first two frame numbers (00 and 01) shall be omitted
from the count at the start of each minute except minutes 00, 10, 20, 30, 40, and 50.
Because the frame rate of a progressive NTSC-time related 60 frames per second television
signal is actually 60/1,001 frames per second, and each time code count references a frame
pair, the same counting mechanism may be applied as well. See Clause 11 for additional
information on this subject.
When drop-frame compensation is applied to an NTSC television time code, the total error
accumulated after one hour is reduced to –3,6 ms. The total error accumulated over a 24-hour
period is –86 ms.
4.3 Colour frame identification in NTSC analogue composite television systems
If colour frame identification in the time code is required, the even units of frame numbers shall
identify colour fields I and II, and the odd units of frame numbers shall identify colour fields III
and IV.
NOTE Even though a component system does not have a colour sequence, the time code may carry colour
sequence information from an original video source so that recoding of a composite signal into a component signal
and back can preserve the original colour sequence relationship.
5 Time representation in 25 frames per second and 50 frames per second
systems
5.1 Definition of real time
In a system running at a frame rate of 25 frames per second, exactly one second of real time
elapses during the scanning of 25 frames. An example of such a system is a 625/50 television
system. In a system running at a frame rate of 50 frames per second, exactly one second of
real time elapses during the duration of 50 frames.
5.2 Time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. For systems operating at 50 frames per second, each frame pair
shall be identified by a unique and complete address consisting of an hour, minute, second,
and frame number.
The hours, minutes, and seconds follow the ascending progression of a 24-hour clock
beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes, and 59 seconds.
The frames (or frame pairs for 50 frames per second systems) shall be numbered successively
0 through 24.
There is no counting mode such as drop frame (which is applicable only to 30 frame counting)
that is applicable to 25 frame counting.
60461 IEC:2010 – 13 –
NOTE See Clause 11 for additional information regarding television systems which operate at frame rates of 50
frames per second.
5.3 Colour frame identification in PAL analogue composite television systems
5.3.1 Colour frame identification
If identification of the eight-field colour sequence in the time code is required, the time address
shall bear a predictable relationship with the eight-field colour sequence (as specified in ITU-R
BT.1700). This relationship can be expressed using either logical or arithmetic notations as
given in 5.3.2 and 5.3.3, respectively.
5.3.2 Logical relationship
Given that the frame and second numbers of the time address are expressed as BCD digit
pairs, the value of the logical expression (A|B) ^ C ^ D ^ E ^ F shall be:
"1" for fields 1, 2, 3, and 4;
"0" for fields 5, 6, 7, and 8
where
A equals the value of the 1's bit of the frame number;
B equals the value of the 1's bit of the second number;
C equals the value of the 2's bit of the frame number;
D equals the value of the 10's bit of the frame number;
E equals the value of the 2's bit of the second number;
F equals the value of the 10's bit of the second number;
| represents the logical OR operation;
^ represents the logical EXCLUSIVE OR operation.
5.3.3 Arithmetic relationship
The remainder of the quotient:
(S +P)
shall be
0 for fields 7 and 8;
1 for fields 1 and 2;
2 for fields 3 and 4;
3 for fields 5 and 6
where
S equals the decimal value of the "seconds" digits of the time address, and
P equals the decimal value of the frames digits of the time address.
6 Time representation in 24-frame systems
6.1 Definitions of real time and NTSC time
6.1.1 Definition of real time
In a system running at a frame rate of 24 frames per second, exactly one second of real time
elapses during the passing of 24 frames. An example of such a system is a film system.
– 14 – 60461 IEC:2010
6.1.2 Definition of NTSC time
In a NTSC-time related television signal operating at 24/1,001 frames per second
(approximately 23,976), straightforward counting at 24 frames per second will yield a deviation
of approximately 86 frames (3,6 s) in one hour of elapsed time.
Where it is desired to maintain a correspondence with 30 frame per second systems the 30
non-drop frame count mode should be used. For additional details refer to Annex B.1.
6.2 Time address of a frame
Each frame shall be identified by a unique and complete address consisting of an hour, minute,
second, and frame number. The hours, minutes, and seconds follow the ascending progression
of a 24 hour clock beginning with 0 hours, 0 minutes, and 0 seconds to 23 hours, 59 minutes,
and 59 seconds. The frames shall be numbered successively 0 through 23.
There is no counting mode such as drop frame (which is applicable only to 30 frame counting)
that is applicable to 24 frame counting.
7 Structure of the time address and control bits
7.1 Numeric code
The numeric code consists of sixteen four-bit groups, eight groups containing time address and
flag bits, and eight four-bit binary groups for user-defined data and control codes.
7.2 Time address
The basic structure of the time address is based upon the BCD system, using units and tens in
digit pairs for hours, minutes, seconds, and frames. Some of the digits are limited to values
that do not require all four bits to be significant. These bits are omitted from the time address
and include the "80s" and "40s" of hours, "80s" of minutes, "80s" of seconds, and the "80s" and
"40s" of frames. Thus the entire time address is coded into 26 bits.
7.3 Flag bits
7.3.1 Definition of flag bits
Six bits are reserved for the storage of flags which define the operational mode of the time and
control code. A device which decodes a time and control code may utilize these flags to
interpret properly the time address and binary group data.
7.3.2 Drop frame flag (NTSC composite television system only)
This flag shall be set to 1 when drop frame compensation is being performed as specified in
4.2.3. When the count is not drop frame compensated, this flag bit shall be set to 0.
7.3.3 Colour frame flag (NTSC and PAL composite television systems only)
If colour frame identification has intentionally been applied to the time and control code by the
original source, as defined in 4.3 or 5.3, this flag shall be set to 1. If this flag is set to logical
zero then there is no implied relationship between the colour frame sequence and the time
address.
NOTE Colour frame identification may be forced by an original source of time and control code by halting the time
address until the colour field to time code relationship is satisfied, after which the time address is incremented
normally each frame. As long as neither the time address counting sequence nor the colour field sequence is
changed, the relationship will remain satisfied.
60461 IEC:2010 – 15 –
7.3.4 Binary group flags
Three flags provide eight unique combinations which specify the use of the binary groups (see
7.4). Three combinations of these flags also specify the time address reference as an external
precision clock time reference (see 7.5) and these also select subsets of the binary group
applications.
NOTE The term binary group flags represents its historical origins, however these flags now also signal time
address count parameters.
7.3.5 Modulation method specific flag
The remaining flag bit is reserved for use by each modulation method. This flag is defined in
8.2.6 and 9.2.5.
7.4 Use of the binary groups
7.4.1 Binary group flag assignments
The binary groups are intended for storage and transmission of data by the users. The format
of the data contained in the binary groups is specified by the value of three binary group flag
bits BGF2, BGF1, and BGF0. The following subclauses define the current assignments of the
binary group flag states.
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