science

SMPTE timecode

SMPTE timecode is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SMPTE timecode rather than just read about it. In short: SMPTE timecode ( or ) is a set of cooperating standards to label individual frames of video or film with a timecode. The system is defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification.

Key takeaways

SMPTE timecode belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SMPTE timecode to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SMPTE timecode from memory before moving on to harder problems.

Reference excerpt

SMPTE timecode ( or ) is a set of cooperating standards to label individual frames of video or film with a timecode. The system is defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification. SMPTE revised the standard in 2008, turning it into a two-part document: SMPTE 12M-1 and SMPTE 12M-2, including new explanations and clarifications. A further revision, SMPTE 12M-3, expanded the standard to higher frame rates. Timecodes are added to film, video or audio material, and have also been adapted to synchronize music and theatrical production. They provide a time reference for editing, synchronization and identification. Timecode is a form of media metadata. The invention of timecode made modern videotape editing possible and led eventually to the creation of non-linear editing systems.

Basic concepts

SMPTE timecode is presented in hour:minute:second:frame format and is typically represented in 32 bits using binary-coded decimal. There are also drop-frame and color framing flags and three extra binary group flag bits used for defining the use of the user bits. The formats of other varieties of SMPTE timecode are derived from that of the linear timecode. More complex timecodes such as vertical interval timecode can also include extra information in a variety of encodings. Sub-second timecode time values are expressed in terms of frames. Common supported frame rates include:

23.98 (24 ÷ 1.001) frame/s (North American HDTV), sometimes also more precisely specified as 23.976. 24 frame/s (film, ATSC, 2K, 4K, 6K) 25 frame/s (PAL (Europe, Uruguay, Argentina, Australia), SECAM, DVB, ATSC) 29.97 (30 ÷ 1.001) frame/s (NTSC American System (U.S., Canada, Mexico, Colombia, et al.), ATSC, PAL-M (Brazil)) 30 frame/s (ATSC) In general, SMPTE timecode frame rate information is implicit, known from the rate of arrival of the timecode from the medium. It may also be specified in other metadata encoded in the medium. The interpretation of several bits, including the color framing and drop frame bits, depends on the underlying data rate. In particular, the drop frame bit is only valid for 29.97 and 30 frame/s

Discontinuous timecode, and flywheel processing Timecodes are 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 with more arbitrary reference. After making a series of recordings, recorded timecodes typically consist of discontinuous segments. For systems using real-time video and audio signals, timecode frames start at or around the vertical sync of a video frame, so it is not possible to know the linear timecode of the current frame until the frame has already gone by. Practical real-time timecode decoders use a "flywheel" algorithm follows the ascending sequence of timecodes, and infer the time of the current frame from that, something which is also useful to skip over bit errors or dropouts in the timecode stream. However, this requires a series of good timecodes to establish the ascending sequence in the first place, and thus a boundary between discontinuous timecode ranges cannot be determined by this algorithm until several subsequent frames have passed. This restriction does not apply to systems that can access both previous and subsequent timecodes to establish a particular frame's timecode. Modern non-linear editing systems are not subject to any of these restrictions, because their video streams are contained within compressed data streams, with timecode information held as metadata.

Drop-frame timecode Drop-frame timecode originates from a compromise introduced when color NTSC video was invented. The NTSC designers wanted to retain compatibility with existing monochrome televisions. To minimize subcarrier visibility on a monochrome receiver it was necessary to make the color subcarrier an odd multiple of half the line scan frequency; the multiple originally chosen was 495. With a 30 Hz frame rate the line scan frequency is (30 × 525) = 15750 Hz. So the subcarrier frequency would have been ⁠495/2⁠ × 15750 = 3.898125 MHz. This was the subcarrier frequency originally chosen, but tests showed that on some monochrome receivers an interference pattern caused by the beat between the color subcarrier and the 4.5 MHz sound intercarrier could be seen. The visibility of this pattern could be greatly reduced by lowering the subcarrier frequency multiple to 455 (thus increasing the beat frequency from approximately 600 kHz to approximately 920 kHz) and by making the beat frequency also equal to an odd multiple of half the line scan frequency. This latter change could have been achieved by raising the sound intercarrier by 0.1% to 4.5045 MHz, but the designers, concerned that this might cause problems with some existing receivers, decided instead to reduce the color subcarrier frequency, and thus both the line scan frequency and the frame rate, by 0.1% instead. Thus the NTSC color subcarrier ended up as 3.57954 MHz (⁠315/88⁠ MHz), the line scan frequency as 15.734265 kHz (⁠9/572⁠ MHz) and the frame rate 29.970029 Hz (⁠30/1.001⁠ Hz). The altered frame rate meant that an hour of timecode at a nominal frame rate of 29.97 frame/s was longer than an hour of wall-clock time by 3.6 seconds (for 29.97 non-drop timecode of 01:00:00:00 drop-frame timecode is 01:00:03;18 and for non-drop 00:59:56:12 drop-frame is 01:00:00;00), leading to an error of almost a minute and a half over a day. To correct this, drop-frame SMPTE timecode was invented. In spite of what the name implies, no video frames are dropped or skipped when using drop-frame timecode. Rather, some of the timecodes are dropped. In order to make an hour of timecode match an hour on the clock, drop-frame timecode skips frame numbers 0 and 1 of the first second of every minute, except when the number of minutes is divisible by ten. This causes timecode to skip 18 frames each ten minutes (18,000 frames @ 30 frame/s) and almost perfectly compensates for the difference in rate (but still accumulates 1 frame every 9 hours 15 minutes). For example, the sequence when frame counts are dropped:

01:08:59:28 01:08:59:29 01:09:00:02 01:09:00:03 For each tenth minute

… excerpt ends here. Continue reading the full article.

Illustrations

SMPTE timecode: 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). — 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).

Worked examples

Example 1 — a first encounter with SMPTE timecode

Start with the simplest possible case. Write down what SMPTE timecode claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SMPTE timecode before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SMPTE timecode ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SMPTE timecode

In research: SMPTE timecode appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SMPTE timecode in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SMPTE timecode is common in secondary-school and first-year university syllabi. It links to neighbouring topics Encodings, SMPTE standards, Timecodes, so understanding it makes those chapters shorter.
In everyday life: Look for SMPTE timecode outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “SMPTE timecode” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study SMPTE timecode in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SMPTE timecode means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SMPTE timecode out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SMPTE timecode in simple terms?

Why does SMPTE timecode matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SMPTE timecode?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SMPTE timecode.