Timecode

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Timecode is an electronic guide track added to film, video or audio material that provides a time reference for editing, synchronisation and identification. Timecode is a form of media metadata.

Basic linear timecode contains binary-coded-decimal hour:minute:second:frame identification and a set of 32 binary-coded 'user bits', as well as drop-frame and colour framing flags and three extra 'binary group flag' bits used for defining the use of the user bits. The formats of other forms of LTC-derived timecodes are derived from that of linear timecode.

Frame rate information is implicit, and is assumed to be known given the rate of arrival of the timecode from the medium, or other metadata encoded in the medium.

Timecode is generated as a continuous stream of sequential data values. In some applications 'wall clock' time is used, in others the time encoded is a notional time offset. After editing, recorded timecode may consist of a number of discontinuous segments. Most timecode processing devices check for internal consistency in the sequence of timecode values, and use simple error correction schemes to correct for short error bursts. As a result, the boundary between discontinuous timecode ranges cannot be determined exactly until several frames of code have been read after the timecode boundary.

More complex time codes such as Vertical interval timecode can also include extra information in a variety of encodings. Time code can have any of a number of frame rates: common ones are

  • 24 fps (film)
  • 25 fps (PAL colour television)
  • 30/1.001 fps (NTSC colour television)
  • 30 fps (American black-and-white television) (obsolete)

"Drop frame" timecode is used in the American NTSC TV system to deal with the fact that there are not an exact number of frames in one second on NTSC television.

'Linear timecode' family of timecodes:

Other related time and sequence codes:

References:

  • 'Timecode: A user's guide, second edition' by John Ratcliff, [Focal Press]
  • 'A Technical Introduction to Digital Video' by Charles Poynton

Timecodes for purposes other than video and audio production:

Used for military, government and commercial purposes.


See also Global Positioning System

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