SMPTE timecode

The system is defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification.

Timecodes are added to film, video or audio material, and have also been adapted to synchronize music and theatrical production.

SMPTE timecode is presented in hour:minute:second:frame format and is typically represented in 32 bits using binary-coded decimal.

In particular, the drop frame bit is only valid for 29.97 and 30 frame/s Timecodes are generated as a continuous stream of sequential data values.

Practical systems watch the ascending sequence of the timecode and infer the time of the current frame from that.

Drop-frame timecode originates from a compromise introduced when color NTSC video was invented.

[b][3] For example, the sequence when frame counts are dropped: For each tenth minute 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 (.)

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 television standard.

The version adopted by SMPTE was developed by Leo O'Donnell while he was working for the National Film Board of Canada.

Leo's version referenced time of day and used an 80-bit word that was derived from rocket telemetry.

SMPTE timecode on a clapperboard
SMPTE timecode signal (A logic value 1 is expressed by a transition at the midpoint of a period. A logic value 0 is expressed by the absence of such a transition.) compared to the outwardly-similar Manchester code (A logic value 0 is expressed by a high-to-low transition, a logic value 1 by low-to-high transition at the midpoint of a period).