SMPTE timecode

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SMPTE timecode is a set of standards that work together to label individual video or movie frames with time codes. This 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.

Timecodes are added to movies, videos or audio materials, and have also been adapted to sync music and theatrical productions. They provide time references for editing, syncing, and identification. Timecode is a form of media metadata. Time code discovery allows the editing of modern videocassettes, and ultimately leads to the creation of non-linear editing systems.

Video SMPTE timecode

Basic concepts

SMPTE timecodes ( or ) contain binary coded decimal hours: minutes: seconds: frame identification and 32 bits for user use. There are also frame-frame frames and color framing flags and three additional binary binary bits used to define the usage of user bits. The other varieties format of the SMPTE time code comes from the longitudinal time code.

Time codes can use any number of frame frequencies. The common ones are:

• 24 frames/second (movie, ATSC, 2k, 4k, 6k)
• 25 frames/second (PAL (Europe, Uruguay, Argentina, Australia), SECAM, DVB, ATSC)
• 29.97 (30 ÃÆ' Â · 1,001 frames/sec (American NTSC System (US, Canada, Mexico, Colombia, etc.), ATSC, PAL-M (Brazil))
• 30 frames/sec (ATSC)

In general, the SMPTE time frame rate information is implicitly, known from the time arrival code of the medium, or other metadata encoded in the medium. Interpretation of several bits, including "framing" and "drop frame" bits, depends on the underlying data rate. Specifically, the frame bit drop only applies to the nominal frame rate of 30 frames/s: see below for details.

More complex timecodes such as vertical interval timecode can also include additional information in various encodings.

Maps SMPTE timecode

Dashed timing code, and flywheel processing

The time code is generated as a continuous stream of consecutive data values. In some applications "clock wall" time is used, another time encoded is notional time. After creating a series of recordings, or after rough editing, the recorded timecode may consist of a disconnected segment.

In general it is not possible to know the linear timecode (LTC) of the current frame until the frame has passed, by that time it is too late to make the editing. The system practically watches the sequence of the ascending time sequence, and deducts the time from the current frame from it.

Because the timecode in the analog system is vulnerable to bit errors and drop-outs, most time code processing devices check internal consistency in the time value code sequence, and use a simple error correction scheme to correct short burst errors. Thus, the boundary between the discontinuous time code ranges can not be determined with certainty until the next few frames or the interrupted sequence of them has passed. For this reason, most video cassette editing attempts to keep the time code of the material recorded on an ongoing basis, so some editing can be repeatedly recorded excessively to the same video.

Although it is possible in digital systems to eliminate the need for flywheel algorithms by adding frame delay to allow time codes to decode before frame processing, this is not done in most practical systems as it will introduce unnecessary frame delays on signal processing lines, and there will still be a need compensate for time code errors in signals coming from analog video or audio systems.

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Stop timecode frame

The time frame of the falling frame comes from a compromise found when a NTSC color video is found. NTSC designers want to maintain compatibility with existing monochrome televisions. To minimize the visibility of the subcarrier on a monochrome receiver, it is necessary to make the color subcarrier an odd multiple of half the frequency of line scanning; some of which originally selected were 495. With a frame frequency of 30 Hz, the frequency of line scanning (30 ÃÆ'â € "525) = 15750 Hz. So the subcarrier frequency should be (495/2 ÃÆ'â € 15750) = 3.898125 MHz. This is the preferred subcarrier frequency, but tests show that in some monochrome receivers, interference patterns caused by beats between the color subcarrier and the 4.5 MHz sound intercarrier can be seen. The visibility of this pattern can be greatly reduced by lowering the subcarrier frequency to 455 (thus increasing the beat frequency from approximately 600 kHz to approximately 920 kHz) and by making the beat frequency also equal to the odd multiple of half the frequency of line scanning. This last change can be achieved by increasing the voice intercarrier by 0.1% to 4.5045 MHz, but the designers, who fear that this may cause problems with some existing receivers, decided to reduce the color subcarrier frequency, and thus both line scanning frequency and frequency of images, with 0.1% instead. Thus the NTSC color subcarrier ends up as 3.57954545 MHz (precisely 315/88 MHz), the line scanning frequency of 15734.27 Hz (exactly 9/572 MHz) and the frame rate of 29.97 Hz (precisely 30/1,001 Hz).

This means that the "clock time code" at a nominal frame rate of 30 frames/s, when played back at 29.97 frames/s is longer than an hour of wall-clock time by 3.6 seconds, which causes errors of almost a minute and a half more in a day.

To fix this, the SMPTE timecode frame drop was created. Regardless of what the name implies, no the video frame is dropped (skipped) using a drop-frame timecode. Instead, some timecodes are dropped. To make one clock timecode match one hour on the clock, the drop-frame timecode skips a frame of numbers 0 and 1 from the first second of every minute except when the number of minutes is divisible by ten (ie when module 10 mins equals zero). (Because cutting editors should be aware of the differences in subcarrier color phase between even and odd frames, it would be helpful to skip the frame number pair.) This achieves an easy-to-track frame drop level of 18 frames every ten minutes (18,000 frames @ 30 frames/s) and almost perfectly compensate for the rate difference, leaving the remaining time error of only 1.0 ppm, about 2.6 frames (86.4 milliseconds) per day.

That is, the drop frame TC drops 18/18000 frame number, equivalent to 1/1000, reaching 30ÃÆ' â € "0.999 = 29.97 frame/s. This is very slightly slower than the actual NTSC frame ratio of 30/1,001 = 29.97 002997 frame/s, which is equivalent to dropping 1/1001 frame numbers. The difference is an additional NTSC frame per 1,000,000 TC frame drop values, which can be ignored.

For example, the order in which the number of frames is dropped:
01: 08: 59: 28
01: 08: 59: 29
01: 09: 00: 02
01: 09: 00: 03

For every 10th minute
01: 09: 59: 28 01: 09: 59: 29
01: 10: 00: 00
01: 10: 00: 01

While the non-drop timecode is displayed with a colon that separates the digit pairs - "HH: MM: SS: FF" - the drop frame is usually represented by a semicolon (;) or dot (.) As a divisor between all pairs of digits - "HH; MM ; SS; FF "," HH.MM.SS.FF "- or just between seconds and frame -" HH: MM: SS; FF "or" HH: MM: SS.FF ". This period is usually used on VTRs and other devices that do not have the ability to display semicolons.

Drop frame timecode is usually abbreviated as DF and non-drop as NDF.

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Framing color and time code

Color framing bits are often used to denote the 1st plane of the color frame, so editing tools can be sure to edit only on the appropriate field boundaries to prevent image corruption.

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Studio and master clock operations

In a television studio operation, an elongated timecode is generated by a master studio synchronization generator, and is distributed from a central point. Center synchronization generators typically take their time from atomic clocks, using either network time or GPS. Studios usually maintain two or three hours, and automatically switch if one fails.

The latest development is to install SMPTE timeline sync timeline on each camera, which eliminates the distribution network for portable settings and on-site shooting.

Longitudinal SMPTE codes are widely used to sync music. Frame rate 30 frames/s is often used for audio in America, Japan, and other countries that rely on a 60 Hz holding frequency and use NTSC standard television. The European Broadcasting Union (EBU) frame standard of 25 frames/s is used throughout Europe, Australia and where the main frequency is 50 Hz, and PAL or SECAM television standards are used.

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SMPTE timecode media

1. Linear timecode, a.k.a. "longitudinal timecode" and "LTC": suitable to be recorded on an audio channel, or with an audio cable. This is how it is distributed in the studio to synchronize recorder and camera. To read LTC, the recording must move, which means LTC is useless when the recording is stationary or almost stationary. This deficiency leads to the development of VITC.
2. Vertical interval timecode, a.k.a VITC (pronounced "vit-view"): recorded directly to VBI (vertical blanking interval) of the video signal on each video frame. The advantage of VITC is that, since this is part of the video playback, it can be read when the recording is stationary.
3. CTL timecode: The SMPTE timecode is embedded in the video record control path.
4. Visible time codes, burning time codes and BITC (pronounced "bit-see") - numbers burned into video images so humans can easily read timing codes. Video tapes duplicated with these "burn-in" time code numbers into videos are known as window dubs .
5. Movie labels, such as Keykode.

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History

Longitudinal timecode and vertical intervals were developed in 1967 by EECO, an electronics company that developed video recorders, and then video production systems. EECO commissioned its intellectual property to permit public use.

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See also

• Linear timecode
• Timecode vertical interval
• Timecode burn
• MIDI time code
• Time code embedded AES-EBU
• Customizable consumer time code
• 2-3 pulldown
• Field of dominance

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References

• John Ratcliff (1999). Timecode: User guide, second edition (third edition.). Press Fokal. ISBN 978-0-240-51539-7.
• Charles Poynton (1996). Digital Video Technical Introduction . John Wiley & amp; Children. ISBNÃ, 0-471-12253-X.

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External links

• Introduction to the Basic Principles of the SMPTE/EBU Time Code
• museum.tv articles about timing and video editing
• Technical Introduction to Timecode by Charles Poynton
• Article about the time code by Chris Pirazzi
• Sync and SMPTE TimeCodes.
• Peter Utz. "Time Code Explained SMPTE". Archived from the original on 2009-02-10.
• Convert between SMPTE hh: mm: ss: ff Code Time and Frame with source code c by Brooks Harris

Source of the article : Wikipedia