Use of timecode in video production
Timecode or TC is the name given to the sequence of numeric codes generated at regular intervals by a timing system under the format of hours:Minutes:Seconds:Frames.
This information is vital for all editing systems and to us easy to understand because is based in the system that we use to measure time. Timecode appears as answer to the need for a system capable to generate a linear timing reference to help in the manipulation and synchronization of video recorded signals as base for its practical use in the processes inherent to the video postproduction industry.
There are two well known types of Timecode, classified in dependency to how the signal is recorded in the media (the tape): Linear Timecode (LTC) and Vertical Interval Timecode (VITC).
The first one encodes SMPTE (Sound and Motion Pictures Television Engineering standard) timecode data as a Manchester-encoded audio signal. Each frame is terminated by a 'sync word' which has a special predefined sync relationship with any video or film content. The sound of linear timecode is a jarring and distinctive noise and has been used as sound-effect shorthand to imply 'telemetry' or 'computers'. Technical care had to be taken with old recording systems based on analog audio to avoid audible 'breakthrough' from the LTC track to the audio tracks that would damage your sound quality.
Vertical Interval Timecode (pronounced "vitsee" or sometimes "vits") is a form of SMPTE timecode embedded as black-and-white bars in a pair of the normally unseen vertical interval lines in a television signal. There can be more than one VITC pair in a single frame of video: this can be used to encode extra data that will not fit in a standard timecode frame. The VITC code is always repeated on two adjacent video lines, one in each field. This internal redundancy is exploited by VITC readers, in addition to the standard timecode "flywheel" algorithm.
For the common user timecode is useful in the process of viewing and logging material because it’s unique relationship with each specific portion of the tape and the images recording in it (assuming that was recorded and kept continuously). You can review and organize the material just writing the number and descriptions in a paper pad of each segment of your interest and assigning individual names to each tape. This image can be later easily re-called when needed during the editing process.
But there are most sophisticated ways to log our material through logging applications that allow creating Edit Decisions List (EDL) that allow to import later the selected video in the editing system. These applications usually work connecting your computer (where the program is installed) to a Video Tape Player. The software allows you to assign names to each tape, set in and out points (reading the timecode recorded in the tape) and user descriptions about the content of the images. The final EDL can be then send to the editor though any media (floppy, CD, memory device, etc) or just attached the file to an email and then imported to the editing equipment where once started the capture process all data will be read and tapes will be requested for ingest. Also timecode is a functional part in old editing systems as a precise method to synchronize all video tape recorders, set input and output points and allow timing calculations (such as duration).
In processes of recording video where synchronization of different cameras is needed the timecode is essential. As an example imagine an event recorded with multiples cameras without a switcher, where we will obtain at the end a different tape and angle from the same action. The cameras can be hooked to sync through externals timecode from one determined as the generator or main reference and we will obtain the same timecode in each tape for the same instant in the live action.
These are just some simplified approach to the utility of timecode. For a professional video producer or editor a deeper approach is needed to understand this key concept for the television industry.