Editing Linear timecode (section)

==Longitudinal timecode data format==

[[File:Timecode-audacity.png|thumb|upright=4|Linear timecode waveform as displayed in Audacity with 80 bit data frame highlighted]]

The basic format is an 80-bit code that gives the time of day to the second, and the frame number within the second.  Values are stored in [[binary-coded decimal]], least significant bit first.
There are thirty-two bits of user data, usually used for a reel number and date.

{|class=wikitable style="text-align:center"
|+ SMPTE linear timecode{{r|BR.780-2}}
! Bit || Weight || Meaning
|rowspan=17|
! Bit || Weight || Meaning
|rowspan=17|
! Bit || Weight || Meaning
|rowspan=17|
! Bit || Weight || Meaning
|rowspan=17|
! Bit || Value || Meaning
|- bgcolor=#ffffcc
| 00 || 1 ||rowspan=4| Frame number<br/>units<br/>(0–9)
| 16 || 1 ||rowspan=4| Seconds<br/>units<br/>(0–9)
| 32 || 1 ||rowspan=4| Minutes<br/>units<br/>(0–9)
| 48 || 1 ||rowspan=4| Hours<br/>units<br/>(0–9)
|bgcolor=#ccffff| 64 ||bgcolor=#ccffff| 0 ||rowspan=16 bgcolor=#ccffff| Sync word,<br/>fixed bit<br/>pattern<br/>0011 1111<br/>1111 1101
|- bgcolor=#ffffcc
| 01 || 2
| 17 || 2
| 33 || 2
| 49 || 2
|bgcolor=#ccffff| 65 ||bgcolor=#ccffff| 0
|- bgcolor=#ffffcc
| 02 || 4
| 18 || 4
| 34 || 4
| 50 || 4
|bgcolor=#ccffff| 66 ||bgcolor=#ccffff| 1
|- bgcolor=#ffffcc
| 03 || 8
| 19 || 8
| 35 || 8
| 51 || 8
|bgcolor=#ccffff| 67 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 04 ||rowspan=4 colspan=2| User bits<br/>field 1
| 20 ||rowspan=4 colspan=2| User bits<br/>field 3
| 36 ||rowspan=4 colspan=2| User bits<br/>field 5
| 52 ||rowspan=4 colspan=2| User bits<br/>field 7
|bgcolor=#ccffff| 68 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 05
| 21
| 37
| 53
|bgcolor=#ccffff| 69 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 06
| 22
| 38
| 54
|bgcolor=#ccffff| 70 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 07
| 23
| 39
| 55
|bgcolor=#ccffff| 71 ||bgcolor=#ccffff| 1
|- bgcolor=#ffffcc
| 08 || 10 ||rowspan=2| Frame number<br/>tens (0-2)
| 24 || 10 ||rowspan=3| Seconds<br/>tens<br/>(0–5)
| 40 || 10 ||rowspan=3| Minutes<br/>tens<br/>(0–5)
| 56 || 10 ||rowspan=2| Hours<br/>tens (0-2)
|bgcolor=#ccffff| 72 ||bgcolor=#ccffff| 1
|- bgcolor=#ffffcc
| 09 || 20
| 25 || 20
| 41 || 20
| 57 || 20
|bgcolor=#ccffff| 73 ||bgcolor=#ccffff| 1
|- bgcolor=#ffffcc
|bgcolor=#ffcccc| 10 ||bgcolor=#ffcccc| D ||bgcolor=#ffcccc| [[SMPTE time code#Drop-frame timecode|Drop frame]] flag.
| 26 || 40
| 42 || 40
|bgcolor=ffcccc| 58 ||bgcolor=ffcccc| BGF1 ||bgcolor=ffcccc| Clock flag
|bgcolor=#ccffff| 74 ||bgcolor=#ccffff| 1
|- bgcolor=#ffcccc
| 11 || C || "Color frame" flag
| 27 ||colspan=2| (flag, see below)
| 43 ||colspan=2| (flag, see below)
| 59 ||colspan=2| (flag, see below)
|bgcolor=#ccffff| 75 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 12 ||rowspan=4 colspan=2| User bits<br/>field 2
| 28 ||rowspan=4 colspan=2| User bits<br/>field 4
| 44 ||rowspan=4 colspan=2| User bits<br/>field 6
| 60 ||rowspan=4 colspan=2| User bits<br/>field 8
|bgcolor=#ccffff| 76 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 13
| 29
| 45
| 61
|bgcolor=#ccffff| 77 ||bgcolor=#ccffff| 1
|- bgcolor=#ccffcc
| 14
| 30
| 46
| 62
|bgcolor=#ccffff| 78 ||bgcolor=#ccffff| 0
|- bgcolor=#ccffcc
| 15
| 31
| 47
| 63
|bgcolor=#ccffff| 79 ||bgcolor=#ccffff| 1
|}
* Bit 10 is set to 1 if [[SMPTE time code#Drop-frame timecode|drop frame]] numbering is in use; frame numbers 0 and 1 are skipped during the first second of every minute, except multiples of 10 minutes.  This converts 30 frame/second time code to the 29.97 frame/second [[NTSC]] standard.
* Bit 11, the [[color framing]] bit, is set to 1 if the time code is synchronized to a color video signal.  The frame number modulo 2 (for NTSC and [[SECAM]]) or modulo 4 (for [[PAL]]) should be preserved across cuts in order to avoid phase jumps in the [[chrominance subcarrier]].
* Bits 27, 43, and 59 differ between 25 frame/s time code, and other frame rates (30, 29.97, or 24).{{r|BR.780-2|p=9}}<ref>{{Citation |mode=cs1 |title=Indian Standard IS: 12429 (Part 1) Time and Control Code for Video Tape Recorders: Part 1 Longitudinal Time Code (LTC) |year=2002 |orig-year=1988 |publisher=[[Bureau of Indian Standards]] |pages=1–3 |url=https://law.resource.org/pub/in/bis/S04/is.12429.1.1988.pdf}}  This is an example of the 25 frame/s bit assignments, which are different from the more commonly seen 30/29.97/24 bit assignments.</ref>  The bits are:
** "Polarity correction bit" (bit 59 at 25 frame/s, bit 27 at other rates): this bit is chosen to provide an even number of 0 bits in the whole frame, including the sync code.  (Since the frame is an even number of bits long, this implies an even number of 1 bits, and is thus an [[even parity]] bit.  Since the sync code includes an odd number of 1 bits, it is an odd parity bit over the data.)  This keeps the phase of each frame consistent, so it always starts with a rising edge at the beginning of bit 0.  This allows seamless splicing of different time codes, and lets it be more easily read with an [[oscilloscope]].<!--It is NOT needed to ensure zero DC bias; biphase encoding takes care of that.-->
** "Binary group flag" bits BGF0 and BGF2 (bits 27 and 43 at 25 frame/s, bits 43 and 59 at other rates): these indicate the format of the user bits.  Both 0 indicates no (or unspecified) format.  Only BGF0 set indicates four 8-bit characters (transmitted [[little-endian]]).  The combinations with BGF2 set are reserved.{{r|BR.780-2|p=7–8}}
* Bit 58, unused in earlier versions of the specification, is now defined as "binary group flag 1" and indicates that the time code is synchronized to an external clock.{{r|BR.780-2|p=7}}  if zero, the time origin is arbitrary.
* The sync pattern in bits 64 through 79 includes 12 consecutive 1 bits, which cannot appear anywhere else in the time code.  Assuming all user bits are set to 1, the longest run of 1 bits that can appear elsewhere in the time code is 10, bits 9 to 18 inclusive.
* The sync pattern is preceded by 00 and followed by 01.  This is used to determine whether an audio tape is running forward or backward.<ref>{{cite web |title=SMPTR Made Simple |publisher=TimeLine Vista, Inc. |year=1996 |page=11 |url=http://faculty.spokanefalls.edu/InetShare/AutoWebs/steveg/SmpteMadeSimple.pdf |quote=The time code reader uses the direction sense bits to determine whether the tape is running forward or backward.}}</ref><ref>{{cite web |title=Synchronisation and SMPTE timecode (time code) |first=Phil |last=Rees |date=15 November 2013 |url=http://www.philrees.co.uk/articles/timecode.htm |access-date=2016-12-25}}</ref>