Timecode (LTC / VITC / MTC)
Definition
Timecode is a time reference, standardised by SMPTE ST 12-1, that labels each video frame with hours, minutes, seconds and frames, so that video, audio, lighting and show control can run on the same clock. LTC (linear timecode) is an audio-frequency signal carried on an XLR cable or an audio track. VITC (vertical interval timecode) is embedded in the vertical blanking interval of analogue and SD video, while in HD-SDI timecode travels as ancillary data (ATC, SMPTE ST 12-2). MTC (MIDI Time Code) carries the same information over MIDI for DAWs and show control. The usual rates are 24, 25, 29.97 DF (drop frame) and 30 fps.
In the field
Drop-frame timecode (29.97 DF) compensates for the 0.1% difference between 30 fps and the 29.97 fps rate of NTSC by skipping frame numbers 00 and 01 at the start of every minute, except every tenth minute; no image is dropped. It is used in 59.94 Hz broadcasting (North America, Japan), while 50 Hz regions such as Europe use 25 fps non-drop. Systems running at different timecode rates drift apart, so the rate is agreed between all departments before the show.
Related lessons
Sources
- SMPTE, Understanding Standards: Time Code : ST 12-1 (LTC, VITC), ST 12-2 (timecode dans les données auxiliaires), drop frame · smpte.org
- Wikipédia, SMPTE timecode : numéros 00 et 01 sautés chaque minute sauf les minutes multiples de dix (pointeur secondaire) · en.wikipedia.org
- Wikipédia, Linear timecode : signal LTC en fréquence audio (pointeur secondaire) · en.wikipedia.org
- Wikipédia, MIDI timecode : transport du timecode sur MIDI (pointeur secondaire) · en.wikipedia.org
- AJA, NTV2 SDK, Ancillary Data : timecode ATC des formats HD selon SMPTE ST 12-2 (anciennement RP 188) · sdkdocs.aja.com