CAMERA



Timecode

Timecode is used to synchronize audio and video or multiple video sources.

In order to allow two different devices to be synchronised with each other, they must both be able to read, process and store timecode data. 

Timecode became a SMPTE standard, and it was initially designed for image editing, but since then is used across the production chain. Timecode consists of the hour, minute, second and frame information, displayed like this: 00: 00: 00: 00 to 23: 59: 59: 24.
The values of hours, minutes and seconds are the same for all recording systems. Only the frame values differ. Widely used frame rates are 24 (film), 25 (PAL) and 29.97 (NTSC).
In NTSC 30 images are recorded in a little over a second ("slow second"). Then colour synchronous signals are attached. In order to return to the "right" time after the post production in the TV station, drop frame timecode (29.97DF) is used. Dropframe means that at each start of the minute, 2 frames are "dropped", ie not recorded. The minute starts with frame xx: 02 instead of frame xx: 00. Only in the minutes 1, 11, 21, 31, 41 and 51 are all frames generated, in order to get back to the real time.

For devices that do not have a permanent link to a timing source, such as film cameras, an optical / acoustic sync point is needed. This is where the clapper board was introduced, and used at the beginning of each take. And the clapper board is still used today as the most direct way to identify the beginning of a take.

As professional video cameras developed, the use of timecode moved more into the dailies and post production pipeline, as synchronisation of audio and video became less of an issue with cameras recording both sources as the same time. Today, timecode is stored in the metadata of the generated media files.

It is important to remember that the time code only specifies a time value. Therefore if multiple cameras are to be synched together, timecode alone is not the only answer. Longer synchronised recordings, such as live concerts, require a constant clocking across devices. This is achieved used a Gen-Lock (the use of a Generator locking device). In studios synchronisation is often via black-burst or word clock.

The basic principle of timecode is a continuous clock which mostly refers to the time of day (24h-Run). On location mobile Time code generators are connected to cameras to provide a common accurate timing value. This allows multiple recordings from different cameras to be easily synchronised on an edit timeline.

Timing systems are available from a number of manufacturers including Ambient, Denecke, Timecode Systems and TentacleSync.

It is important that the accuracy of the clocks used is less than a frame difference per 24h and the cameras are always synced to the same time as that of the audio recorder.

For audio recording and post production (when not recorded in camera), almost all professional multi-track recorders have a precise time code generator, which acts as a "master clock" on the set. Some sound recording devices even have Ambient Lockit built in.

With the increase in use of DSLR cameras, the problem of  picture and sound synchronisation reappeared.  Since DSLRs often don’t include high quality audio inputs, the sound often has to be recorded externally. DSLRs do not always include a TC input either, there is an alternate solution, where the required TC is delivered as an audio tone timecode to record a soundtrack on the camera. This timecode value is now not included in the metadata of the video clip but is "encoded" as an audio file on the audio track. This requires special software which reads the TC from the Audio track and writes in the metadata of the video clips.

Some editing programs already provide this option with a menu item, such as Avid Media Composer with the command "read timecode from audio", and other third party tools are also available.

An alternative approach is to use Plural Eyes by Red Giant. This tools makes use of all soundtracks recorded at the location. As long as all media to be synchronized contains audio tracks, the tracks can be used by the software for comparison purposes. This enables more flexible shooting, however a professional TC workflow is often preferable if possible.

At time of writing, SMPTE are exploring the evolution of timecode, through the development of a new standard called Time Labels.