The most complex part of telecine is the
synchronization of the mechanical film motion and the electronic video signal. Every time the video (tele) part of the telecine samples the light electronically, the film (cine) part of the telecine must have a
frame in perfect registration and ready to photograph. This is relatively easy when the film is photographed at the same
frame rate as the video camera will sample, but when video and film frame rates differ, a sophisticated procedure is required.
2:2 pulldown In countries that use the
PAL or
SECAM video standards, film destined for television is photographed at 25 frames per second. The PAL video standard broadcasts at 25 frames per second, so the transfer from film to video is simple; for every film frame, one video frame is captured. Theatrical features originally photographed at 24 frames per second are shown at 25 frames per second. While this is usually not noticed in the picture, the 4% increase in playback speed causes a slightly noticeable increase in
audio pitch by about 0.707
semitones. This can be corrected using
time stretching algorithms, which speed up audio while preserving pitch. 2:2 pulldown is also used to transfer shows and films photographed at 30 frames per second, like
Friends and
Oklahoma! (1955), to
NTSC video, which has ≈59.94 Hz scanning rate. This requires playback speed to be slowed by a tenth of a percent.
2:3 pulldown In the United States and other countries where television uses the
59.94 Hz vertical scanning frequency, video is broadcast at ≈29.97 . For the film's motion to be accurately rendered on the video signal, a telecine must use a technique called the
2:3 pulldown, also known as
3:2 pulldown, to convert from 24 to ≈29.97 . The term
pulldown comes from the mechanical process of
pulling (physically moving) the film downward within the film portion of the transport mechanism, to advance it from one frame to the next at a given rate (nominally 24 ). This is accomplished in two steps. The first step is to slow down the film motion by NTSC's ratio to (≈23.976) . The difference in speed is imperceptible to the viewer. For a two-hour film, play time is extended by 7.2 seconds. If the total playback time must be kept exact, a single frame can be dropped every 1000 frames. The second step of the 2:3 pulldown is distributing cinema frames into video fields. At 23.976 , there are four frames of film for every five frames of 29.97 video: : \frac{23.976}{29.97} = \frac{4}{5} These four film frames are
stretched into five video frames by exploiting the
interlaced nature of 60 Hz video. For every video frame, there are actually two incomplete images or
fields, one for the odd-numbered lines of the image, and one for the even-numbered lines. There are, therefore, ten fields for every four film frames, which are called
A,
B,
C, and
D. The telecine alternately places frame
A across two fields, frame
B across three fields, frame
C across two fields and frame
D across three fields. This can be written as A-A-B-B-B-C-C-D-D-D or 2-3-2-3 or simply 2–3. The cycle repeats itself completely after four film frames. A
3:2 pulldown pattern is identical to the one described above except that it is shifted by one frame. For instance, a cycle that starts with film frame B yields a 3:2 pattern: B-B-B-C-C-D-D-D-A-A or 3-2-3-2 or simply 3–2. In other words, there is no difference between the 2-3 and 3-2 patterns. In fact, the
3-2 notation is misleading because, according to SMPTE standards, for every four-frame film sequence, the first frame is scanned twice, not three times. The above method is a
classic 2:3, which was used before frame buffers allowed for holding more than one frame. The preferred method for doing a 2:3 creates only one dirty frame in every five (i.e., 3:3:2:2 or 2:3:3:2 or 2:2:3:3); while this method has slightly more
judder, it allows for easier upconversion (the dirty frame can be dropped without losing information) and a better overall compression when encoding. The 2:3:3:2 pattern is supported by the
Panasonic DVX-100B video camera under the name "Advanced Pulldown". Note that just fields are displayed—no frames, hence no dirty frames—in an interlaced display, such as on a CRT. Dirty frames may appear in other methods of displaying the interlaced video.
Euro pulldown A new method called 2:2:2:2:2:2:2:2:2:2:2:3, Euro, 12:1 or 24:1 pulldown, can be used in order to convert 24 material to 25 . Usually, this involves a film to PAL transfer without the aforementioned 4% speedup. For film at 24 , there are 24 frames of film for every 25 frames of PAL video. In order to accommodate this mismatch in frame rate, 24 frames of film have to be distributed over 50 PAL fields. This can be accomplished by inserting a pulldown field every 12 frames, thus effectively spreading 12 frames of film over 25 fields (or
12.5 frames) of PAL video. This method was born out of a frustration with the faster, higher-pitched soundtracks that traditionally accompanied films transferred for PAL and SECAM audiences. A few motion pictures are beginning to be telecined this way. It is particularly suited for films where the soundtrack is of special importance.
Other pulldown patterns Similar techniques must be used for films shot at
silent speeds of less than 24 , which includes home movie formats (the standard for
Standard 8 mm film was 16 fps, and 18 fps for
Super 8 mm film) as well as
silent film (which in 35 mm format usually was 16 fps, 12 fps, or even lower). • 16 (actually 15.984) to NTSC 30 (actually 29.97): pulldown should be 3:4:4:4 or the film may be run at 15 (actually 14.985) then pulldown should be 4:4. As motion pictures shot at this framerate are silent, there is no audio that is affected. • 16 to PAL 25: pulldown should be 3:3:3:3:3:3:3:4 (if the film playback rate is increased to [1,000 frames per minute)] pulldown is simplified to 3:3) • 18 (slowed to 17.982) to NTSC 30: pulldown should be 3:3:4 • 20 (slowed to 19.98) to NTSC 30: pulldown should be 3:3 • 20 to PAL 25: pulldown should be 3:2 • 27.5 to NTSC 30: pulldown should be 3:2:2:2:2 • 27.5 to PAL 25: pulldown should be 1:2:2:2:2 Also, other patterns have been described that refer to the
progressive frame rate conversion required to display 24 video (e.g., from a DVD player) on a progressive display (e.g., LCD or plasma): • 24 to 96 (4× frame repetition): pulldown is 4:4 • 24 to 120 (5× frame repetition): pulldown is 5:5 • 24 to 120 (3:2 pulldown followed by 2× deinterlacing): pulldown is 6:4
Mainframe Entertainment used a novel process for its TV shows. They are rendered at exactly 25.000 frames per second; then, for PAL/SECAM distribution, ordinary 2:2 pulldown is applied, but for NTSC distribution, 199 fields out of every 1001 are repeated. This brings the refresh rate from 25 to exactly , or ≈59.94, fields per second, with no change whatsoever in speed, duration, or audio pitch.
Telecine judder The
2:3 pulldown telecine process creates a slight error in the video signal compared to the original film frames that can be seen in the
2:3 pulldown diagram above. This is one reason why films viewed on typical NTSC home equipment may not appear as smooth as when viewed in a cinema and on PAL home equipment. The effect is particularly apparent in scenes that feature slow, steady camera movements. These appear slightly jerky when viewed in material that has been through the telecine process. The phenomenon is commonly referred to as
telecine judder. Reversing the 2:3 pulldown telecine is discussed below. PAL material in which 2:3 (Euro) pulldown has been applied suffers from a similar lack of smoothness, though this effect is not usually called
telecine judder. Effectively, every 12th film frame is displayed for the duration of three PAL fields (60 milliseconds), whereas the other 11 frames are each displayed for the duration of two PAL fields (40 milliseconds). This causes a slight
hiccup in the video about twice a second.
Reverse telecine Some
DVD players,
line doublers, and
personal video recorders are designed to detect and remove 2:3 pulldown from telecined video sources, thereby reconstructing the original 24 film frames. Many video editing programs, such as
AviSynth, also have this ability. This technique is known as
reverse telecine,
inverse telecine (
IVTC),
reverse pulldown or
detelecine. Benefits of reverse telecine include high-quality non-interlaced display on compatible display devices and the elimination of redundant data. Reverse telecine is crucial when acquiring film material into a
digital non-linear editing system since these machines produce
edit decision lists which refer to specific frames in the original film material. When video from a telecine is ingested into these systems, the operator usually has available a
telecine trace, in the form of a text file, which gives the correspondence between the video material and film original. Alternatively, the video transfer may include telecine sequence markers
burned in to the video image along with other identifying information such as time code. It is also possible, but more difficult, to perform reverse telecine without prior knowledge of where each field of video lies in the 2:3 pulldown pattern. This is the task faced by most consumer equipment, such as line doublers and personal video recorders. Ideally, only a single field needs to be identified, the rest following the pattern in lock-step. However, the 2:3 pulldown pattern does not necessarily remain consistent throughout an entire program. Edits performed on film material after it undergoes 2:3 pulldown, e.g., in NTSC format, can introduce
jumps in the pattern if care is not taken to preserve the original frame sequence. Most reverse telecine algorithms attempt to follow the 2:3 pattern using image analysis techniques, e.g., by searching for repeated fields. Algorithms that perform 2:3 pulldown removal also usually perform the task of
deinterlacing. It is possible to algorithmically determine whether video contains a 2:3 pulldown pattern or not, and selectively do either reverse telecine (in the case of film-sourced video) or simpler deinterlacing (in the case of native video sources). ==Telecine hardware==