1、 Rec. ITU-R BR.780-2 1 RECOMMENDATION ITU-R BR.780-2*Time and control code standards, for production applications in order to facilitate the international exchange of television programmes on magnetic tapes*(1992-2002-2005) Scope This Recommendation defines linear time code (LTC) and vertical interv
2、al time code (VITC) for various applications. The Recommendation also defines the line number of the TV signal where the VITC should be inserted. The ITU Radiocommunication Assembly, considering a) that to assist in the location of required sequences on tape for editing programmes, to enable complex
3、 computer-controlled video tape operations to be undertaken, and to synchronize programme elements stored on different supports, the recording of time and control data on tape is beneficial; b) that two types of time and control codes exist: the code recorded on a longitudinal track with audio chara
4、cteristics (linear time code (LTC); this time code may be distributed in a similar fashion to audio signals; the code recorded as a signal inserted in the field-blanking period of the video signal (vertical interval time code (VITC); this signal may be present as part of the video signal on signal i
5、nterfaces; c) that the VITC can be distributed via the serial digital interface and recorded on digital video tape recorders (VTRs) in the vertical interval as “digital vertical interval time code”; d) that the VITC or the LTC can also be recorded as data in the ancillary data space in VTRs as speci
6、fied in Recommendation ITU-R BT.1366, recommends 1 that for production applications, in order to facilitate the international exchange of television programmes on magnetic tape, the parameters defined in Annex 1 should be implemented. *Radiocommunication Study Group 6 made editorial amendments to th
7、is Recommendation in 2001 in accordance with Resolution ITU-R 44. *International programme exchange is defined as the transmission of television or sound programme material (or components thereof) among professional parties in different countries. It should be based on internationally agreed and wid
8、ely employed technical standards or operating practices, except by prior bilateral agreement among the parties involved. 2 Rec. ITU-R BR.780-2 Annex 1 This Recommendation defines a time and control code for use in television, film and accompanying audio systems operating at 60, 59.94, 50, 30, 29.97,
9、 25, 24 and 23.98 frames/s (fps). Section 4 describes the structure of the time address and control bits of the code, and sets guidelines for storage of user data in the code. Defined in this Recommendation is the modulation method for LTC, and the modulation method for inserting the time code into
10、the vertical interval of a television signal. The time code signal may perform different functions depending upon the application. In some applications the time code signal will be a label to identify discrete frames and may not indicate real time, or time of day. In other applications real time may
11、 be indicated, with the caveat that accuracy of the displayed time may not meet all requirements Normative references Recommendation ITU-R BT.470 Conventional Television Systems (Annex 1). Recommendation ITU-R BT.601 Studio encoding parameters of digital television for standard 4:3 and wide-screen a
12、spect ratios. Recommendation ITU-R BT.709 Parameter values for the HDTV standards for production and international programme exchange. Recommendation ITU-R BT.1543 1 280 720, 16 9 progressively-captured image format for production and international programme exchange in the 60 Hz environment. Standa
13、rd SMPTE 170M-2004. Television Composite Analogue Video Signal NTSC for Studio Applications (see Recommendation ITU-R BT.1700). For the purpose of this Recommendation the following nomenclature applies: Linear time code (LTC) LTC refers to the linear time code modulation system (referred to as the l
14、ongitudinal track application of time and control code). Vertical interval time code (VITC) VITC refers to the modulation system used to insert the time code signal in the vertical blanking interval of a television signal. Digital vertical interval time code (D-VITC) D-VITC is a digitized version of
15、 VITC. Binary coded decimal (BCD) The binary coded decimal (BCD) system is a means for encoding decimal numbers as groups of binary bits. Each decimal digit (0-9) is represented by a unique four-bit code. The four bits are weighted with the digits decimal weight multiplied by successive powers of tw
16、o. For example, the bit weights for a units digit would be 1 20, 1 21, 1 22and 1 23, while the bit weights for a tens digit would be 10 20, 10 21, 10 22and 10 23. Real time In a system running at an integer number of N fps, exactly one second of real time elapses during the passage of N frames. Rec.
17、 ITU-R BR.780-2 3 Drop frame time (DFT) In a television system running at a frame rate of N/1.001 fps, one second of time elapses during the scanning of N television frames. Because of the difference in frame rates, the relationship between real time and drop frame time is: 1 = secDFT= 1.001 secREAL
18、 1 Time address representation in 30 and 30/1.001 framesystems 1.1 Time address of a frame Each TV 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 h clock begin
19、ning with 0 h 0 min 0 s to 23 h 59 min 59 s. The frames shall be numbered successively according to the counting mode (drop frame or non-drop frame) as described below. 1.2 Non-drop frame Frames numbers shall increment 0 through 29, successively. When the non-drop frame mode is active the drop frame
20、 flag contained in the time code signal shall be set to zero. 1.3 Drop frame DFT time The field rate of an 60/1.001 television signal is 30/1.001 fps, counting at 30 ( 29.97) fps will yield an error of approximately 108 frames (3.6 secEA) in 1 h of true clock time (i.e. time address lags clock time)
21、. Drop frame time code, is a technique to minimize the drift between clock time and the time indicated by the time code. To minimize the time error introduced by the 60/1.001 field rate , the first two frame numbers (00 and 01) shall be omitted from the frame count at the start of each minute except
22、 minutes 00, 10, 20, 30, 40 and 50. When drop-frame compensation is applied to a 30/1.001 fps time code, the total error accumulated after one hour is reduced to 3.6 ms. The total error accumulated over a 24 h period is nominally plus 86 ms. (i.e. time address leads clock time). When drop frame comp
23、ensation is being performed the drop frame flag shall be set to one as specified in 5.3.1. 1.4 Colour frame identification in NTSC 525/59.94 television system When colour frame identification in the time code is required, the even units of frame numbers shall identify colour fields I and II, and the
24、 odd units of frame numbers shall identify colour fields III and IV as defined by SMPTE 170M-2004. The colour frame flag shall be set to one when the colour frame relationship to the time code is in effect. 4 Rec. ITU-R BR.780-2 2 Time address representation in 25-frame systems 2.1 Time address of a
25、 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 h clock beginning with 0 h 0 min 0 s to 23 h 59 min 59 s. The frames shall be numbered successively
26、0 through 24. 2.2 Colour frame identification in PAL 625/50 television systems 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 Recommendation ITU-R BT.470. T
27、his relationship can be expressed using either logical or arithmetic notations. The colour frame flag shall be set to one when the colour frame relationship to the time code is in effect. 2.3 Logical relationship Given that the frame and second numbers of the time address are expressed as BCD digit
28、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 = value of the 1s bit of the frame number; B = value of the 1s bit of the second number; C = value of the 2s bit of the frame number; D = value of the 10s bit of the fr
29、ame number; E = value of the 2s bit of the second number; F = value of the 10s bit of the second number; | represents the logical OR operation; represents the logical Exclusive OR operation. 2.4 Arithmetic relationship The remainder of the quotient of the division (S + P)/4- 0 for fields 7 and 8; 1
30、for fields 1 and 2; 2 for fields 3 and 4; 3 for fields 5 and 6. where: S = decimal value of the seconds digits of the time address and P = decimal value of the frames digits of the time address. Rec. ITU-R BR.780-2 5 3 Time address representation in 24-frame systems 3.1 Time address of a frame Each
31、TV or film 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 h clock beginning with 0 h 0 min 0 s to 23 h 59 min 59 s. The frames shall be numbered successively 0
32、 through 23. 3.2 Operation at 24/1.001 (23.98) Hz (24/1.001 Hz) There is no drop frame mode for 24/1.001 applications. Where it is desired to maintain a correspondence with 30-frame systems during a conversion to 30 frames, the 30 non-drop frame count mode should be used. For additional details refe
33、r to Appendix 2 to Annex 1, 2. 3.3 Operation at 24.0 Hz For systems where the TV and film frame rate is 24.0 Hz there is no systematic drift of the time code address relative to clock time. Where it is desired to maintain a correspondence with 25 frame systems the techniques described in Appendix 2
34、to Annex 1, 2 mode should be used. 4 Time address representation in 50 and 60 frame progressive systems 4.1 Time address of a frame Since the frame rate of 50/60 progressive systems exceeds the frame count capacity of the time code address, the count is constrained to increment every second frame. E
35、ach pair of progressive frames shall be identified by a unique and complete address consisting of an hour, minute, second and frame number. Figure 1 shows an example of frame labelling for these systems. FIGURE 1 Example of frame labelling for 50 and 60 fps systems 6 Rec. ITU-R BR.780-2 Where the ti
36、me code is VITC the field mark flag shall be used to identify each of the frames as described in 6.16.4.4. Where the time code is modulated as LTC, the time code shall be aligned to start at the beginning of the first frame of the pair of frames and to finish at the end of the second frame. The indi
37、vidual frames may be identified by their timing relative to the LTC with the first frame being aligned with LTC bits 0 through 39 and the second frame aligned with LTC bits 40 through 79. 5 Structure of the time address and control bits 5.1 Digital code The digital code consists of sixteen 4-bit gro
38、ups, eight groups containing time address and flag bits, and eight 4-bit binary groups for user-defined data and control codes. 5.2 Time address The basic structure of the time address is based upon the BCD system, using units and tens digit pairs for hours, minutes, seconds and frames. Some of the
39、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. The entire time address is coded into 26 bits. 5.3 Flag bits Six bits are
40、 reserved for the storage of flags which define the operational mode of the time and control code. A device that decodes a time and control code may utilize these flags to interpret properly the time address and binary group data. 5.3.1 Drop frame flag (29.97 Hz or 59.94 Hz systems only) This flag s
41、hall be set to one when drop frame compensation is being used. When the count is not drop frame compensated, this flag bit shall be set to zero. 5.3.2 Colour frame flag (525/59.94 and 625/50 systems only) If colour frame identification has been applied to the time and control code this flag shall be
42、 set to one. 5.3.3 Binary group flags Three flags provide eight unique combinations that specify the use of the binary groups (see 5.4.). Three combinations of these flags also specify the time address reference as being related to clock time and these also select subsets of the binary group applica
43、tions. 5.3.4 Modulation method specific flag The remaining flag bit is reserved for use by each modulation method. This flag is defined in 6.7 for LTC and 6.16.4 for VITC. 5.4 Use of the binary groups The binary groups are intended for storage and transmission of data by users. The format of the dat
44、a contained in the binary groups is specified by the value of three binary group flag bits BGF2, BGF1 and BGF0. The following clauses define the current assignments of the binary group flag states. Table 1 summarizes the present assigned combinations. Rec. ITU-R BR.780-2 7 TABLE 1 Binary group flag
45、assignments BGF2 BGF1 BGF0 Time address Binary group Reference Section 0 0 0 Unspecified Unspecified 5.5 0 0 1 Unspecified 8-bit codes 5.7 1 0 0 Unspecified Date and time zone 5.9 1 0 1 Unspecified Page/line 5.11 0 1 0 Clock time Unspecified 5.6 0 1 1 Unassigned Reserved 5.8 1 1 0 Clock time Date an
46、d time zone 5.10 1 1 1 Clock time Page/line 5.12 5.5 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 charact
47、er set. If the character set used for the data insertion is unspecified, the 32 bits within the eight binary groups may be assigned without restriction. 5.6 Character set not specified and clock time (BGF2=0, BGF1=1, BGF0=0) This combination specifies that the time address is referenced to an extern
48、al clock and signifies 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 without restriction. 5.7 Eight-bit character set and unspecified clock time (BGF2=0, BGF1=0, BGF0=1) This combination signi
49、fies 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 zero. 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
