Linear Timecode - Longitudinal Timecode Data Format

Longitudinal Timecode Data Format

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.

SMPTE linear timecode
Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Value	Meaning
00	1	Frame number units (0–23, 24, or 29)	16	1	Seconds units (0–59)	32	1	Minutes units (0–59)	48	1	Hours units (0–23)	64	0	Sync word, fixed bit pattern 0011 1111 1111 1101
01	2		17	2		33	2		49	2		65	0
02	4		18	4		34	4		50	4		66	1
03	8		19	8		35	8		51	8		67	1
04	User bits field 1		20	User bits field 3		36	User bits field 5		52	User bits field 7		68	1
05			21			37			53			69	1
06			22			38			54			70	1
07			23			39			55			71	1
08	10	Frame number tens	24	10	Seconds tens (0–59)	40	10	Minutes tens (0–59)	56	10	Hours tens	72	1
09	20	Frame number tens	25	20		41	20		57	20	Hours tens	73	1
10	D	Drop frame flag.	26	40		42	40		58	0	Reserved, zero	74	1
11	C	"Color frame" flag	27	P	Even parity bit	43	1	Binary group flag	59	2	Binary group flag	75	1
12	User bits field 2		28	User bits field 4		44	User bits field 6		60	User bits field 8		76	1
13			29			45			61			77	1
14			30			46			62			78	0
15			31			47			63			79	1

Bit 10 is set to 1 if 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.
Bit 27, the "bi-phase mark-correction bit" is set to provide an even number of 0 bits in the whole frame, including the sync code. (As there are an even number of bits, this corresponds to the even parity rule of an even number of 1 bits.) This ensures zero net DC bias, and keeps the phase of each frame consistent so that it may be more easily read with an oscilloscope.
Bits 43 and 59, the "binary group flag" bits, indicate the format of the user bits. 0 indicates no (or unspecified) format, while 1 indicates 4 8-bit characters. Values of 2 and 3 (i.e. bit 59 set) are reserved.
Bit 58 is unassigned, should always be transmitted as zero, and ignored on reception.
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.

Read more about this topic: Linear Timecode