24p
Encyclopedia
In video technology, 24p refers to a video format that operates at 24 frames per second (typically, 23.976 frames/s when using equipment based on NTSC
frame rates) frame rate with progressive scan
ning (not interlaced). Originally, 24p was used in the non-linear editing of film
-originated material. Today, 24p formats are being increasingly used for aesthetic reasons in image acquisition, delivering film-like motion characteristics. Some vendors advertise 24p products as a cheaper alternative to film acquisition.
When working entirely within the digital non-linear domain, 24p material is more easily handled than material of higher frame rates. 24p material requires care when it is processed using equipment designed for standard video frame rates.
There are two common workflow
s for processing 24p material using video equipment, one using PAL
frame rates, and the other using NTSC
frame rates. Of these two, the PAL route is the simpler, but each has its own complications.
format with the same methods used to convert film to PAL. The most popular method is to speed up the material by 25/24 (4%). Each 24p frame will take the place of two 50i
fields
. This method incurs no motion artifacts
other than the slightly increased speed, which is typically not noticeable. As for audio, the ~4% increase in speed raises the pitch
by 0.7 of a semitone
, which again typically is not noticed. Sometimes the audio is pitch shifted
to restore the original pitch.
If 24p footage cannot be sped up, (for example if it were coming through a live NTSC
or HD
feed
) it instead can be converted in a pattern
where most frames were held on screen for two fields, but every half second a frame would be held for three fields. Thus the viewer would see motion stutter twice per second. This was the common result when programs were shot on film or had film portions, edited on NTSC, and then shown in PAL countries (mostly music video
s). NTSC to PAL conversion also tends to blur
each film frame into the next, and so is seen as a sub-optimal way to view film footage.
30p
can be preferable over 24p since performing a standards conversion to 25i PAL has fewer technical complexities - any NTSC-PAL converter
will do. The larger differences between the 30p and 25i framerates will cause less noticeable motion artifacts upon conversion.
The original film Keykode
and 24frame/s audio timecode can be then be reconciled with the 25frame/s telecine timecode by the generation of a telecine log file containing this information. Again, once the non-linear editor has this information, editing can be performed entirely in terms of 24frame/s timecode, and the Keykode information preserved for either film cutting or digital intermediate
post-production of scanned film images.
Because sound is recorded separately from moving pictures in 24p projects, there are no problems regarding synchronization or audio pitch: the audio material is simply ingested separately from the moving picture material at its natural rate, and synchronized within the non-linear editor.
At standard analog NTSC video rates (29.97 frames per second) a full "interlaced" frame, unlike a progressive frame, is nearly 1/30th of a second and is composed of two separate "fields," each field nearly 1/60 second. The first field (the odd field) contains visible scan lines 21-263 and the second field (the even field) contains visible scan lines 283-525. What is seen onscreen is two of these fields, "interlaced" together, to produce a single full frame. This comes from the proper longhand designation being vertical resolution, followed by the interlaced/progressive notation, and then the frame rate. So typical DV video is correctly listed as 480i/30. The long hand for 24p is 480p/24. Often the resolution is dropped and the i/p designation moved after the frame rate for shorthand.
24p cameras do not, as NTSC video cameras do, shoot 30 interlaced frames per second (60 fields); they shoot 24 full progressive frames per second.
24p material can be recorded directly into formats that support the framerate. Some of the emerging HD formats support the 24p framerate in addition to 60i and 50i (PAL). Previously, few formats supported 24p and the industry used workarounds to work with 24p footage with 60i equipment.
To record 24p material onto a 60i format (i.e. any NTSC-based format), pulldown is typically added to 'pad' the 24 frames into 60 fields. This is done by taking every frame and splitting it into two fields. Then, every second frame has one of its fields duplicated, resulting in three fields. The fields are then played back in that pattern – 2-3-2-3-2-3-2-3-2-3-2-3-2-3 … and so on. The resulting video becomes a 60i stream and can be displayed on NTSC monitors. However, the aesthetic of 24p motion is retained and the footage does not have the motion of typical 60i video.
This 3:2 pulldown is the same process that is used when transferring film into video
.
Any editing application which supports NTSC video can be used to edit footage employing the 3:2 pulldown scheme. It can be captured as a standard 60i file and edited like footage from any other camera, while still retaining its 24p aesthetic. There can be issues when editing the footage as 60i, however, including choppiness in short transitions or fades, and also a mismatch in the motion characteristics of the footage and any graphics which may be added to it, such as text or logos. So, while 24p footage can be edited as 60i, it is usually better to edit the footage on a 24p timeline with the pulldown removed.
Most current prosumer-level editing applications which edit native 24p can remove the 3:2 pulldown for editing in native 24p, although some cannot. However, this is not ideal; the removal of the 3:2 pulldown involves reconstruction of every fourth frame from two different field groups, which can cause a generational loss and some banding problems if the application doesn't interpret the footage properly. Therefore, using the 3:2 pulldown scheme is not ideal when planning to edit on a 24p timeline.
Note: "3:2 pulldown" has a cadence of 2-3-2-3-2-3..., but in the industry is called "3:2 pulldown", even though the cadence is 2-3. Some people use the term "2:3 pulldown", which corresponds to the cadence, but is not normally used in the industry for the technique.
camcorder. Instead of padding the frames into a repeating 3:2 pattern, the frames are padded into a 2:3:3:2 pattern. This pattern is specific to the NTSC DV format, and would serve no purpose in native 24p formats.
It converts the first frame into two fields, the second into three fields, the third into three fields, and the fourth into two fields. It then repeats this pattern for every group of four frames that follows. This pulldown pattern is used to avoid segmenting a 24p frame into two different 60i fields that exist in two different 60i frames. When a 24p frame is split up and recorded into separate 60i fields, interlacing artifacts can exist in the 60i "frames" (i.e. two fields). These artifacts decrease the compression efficiency of DV
and can result in cycles of efficient compression followed by less-efficient compression. The advanced pulldown scheme avoids this as every 24p frame can be found intact within the resulting sequence of 60i frames, yet the compression efficiency remains the same as with 3:2 pulldown.
When editing 24pA footage, conversion from 60i back to the original 24p is very efficient. It only requires blending the fields made from the frames back into full frames. Then, only every fifth frame will be made up of fields from two different frames, and that frame can be discarded, leaving only the other four full frames. In order for this to work properly, the DVX100 camera records video in chunks of five video frames. This ensures that each clip has regular and predictable cadence.
Because the 2:3:3:2 scheme was devised for efficient pulldown removal for editing, and because 24p editing applications more universally support its removal, it should always be used when planning to edit in native 24p.
Editing systems need specific support for the 24pA format to be able to detect and remove the pulldown properly so that the 24p frames can be edited in a 24p timeline. Many but not all prosumer and professional-level non-linear editing systems are able to recognize and remove this advanced pulldown scheme. However, among the editing applications able to remove pulldown and edit in native 24p, it is more common for them to have support for 24pA 2:3:3:2 pulldown than for standard 24p 3:2 pulldown removal.
Still other editing applications have the option for editing on a 24p timeline, and will accept footage where the pulldown has already been removed in another application.
Remember that although computer editing systems may refer to "24p", usually the precise frame rate is 23.976 frame/s. To add to confusion, the popular editing program Final Cut Pro refers to 23.976 as "23.98" in menus and dialogs, even though it correctly works with the footage at the 23.976 frame rate.
Also because the 2:3:3:2 pulldown scheme was devised in order to make pulldown removal for editing in native 24p more efficient, the pulldown arrangement is not ideal for watching footage. There can be exaggerated stutters in motion, because the frames which are split into three fields are not only onscreen for 50% longer than the other frames, they are back-to-back. As such, 2:3:3:2 pulldown should be used only when a native 24p edit is planned, and not for final viewing. This includes when shooting the footage initially, and also when printing back to tape from an NLE.
Diagram here
can remove these artifacts, but certain methods will cause up to half the footage's vertical resolution to be lost. Adaptive de-interlacing schemes only de-interlace areas of high motion, hence preserving resolution in stationary areas. More advanced techniques can be used to mitigate problems such as aliasing from the temporal displacement between the 60i fields.
to extrapolate 24 frames of information from 60 frames while compensating for the time displacement between the two. For example, in one second of 60i footage, each image is captured at 1/60 second, which does not perfectly align with images that would have been captured 24 times per second. Simply "cherry picking" 24 images out of 60 does not present 24 frames with perfect temporal consistency, since more or less time may have elapsed between frames. The result is a slightly jittery picture, which appears to jitter in a cyclic fashion. Optical flow algorithms will analyze the footage and make corrections to the picture in order to better "fit" each frame into the new 24 frame sequence. The resulting footage is much smoother because it simulates equal exposure time between frames.
For best results, footage should be deinterlaced and frame-doubled to 60p. This preserves all of the footage's temporal information, which is key in determining what the "missing" points in time should look like when converting to 24 frame/s.
The last step is to compensate for the lack of motion blur
in the 60i footage. Since the images were captured at 1/60 second, there is less motion blur between images than there would have been if shot at 24 frame/s with a 180° shutter (i.e. 1/48 second exposure time). Optical flow is used to introduce motion blur between frames, mimicking the motion blur present when shooting the standard 180° shutter angle. This method of creating motion blur is far more realistic than simple frame blending, which is simple to implement and usually a standard feature in most non-linear editing programs.
The optical flow method also works with 30p footage and is currently the best option for 30p to 24p conversion.
the 60p half-resolution result to VirtualDub for further processing (specifically, adjusting field height using the "field bob" filter, resizing back to full resolution and then outputting at 24 frame/s). The reason AviSynth must be used is because VirtualDub cannot split the fields into a 60p sequence on its own, and this technique requires 60p input.
, every fourth frame is repeated. This scheme is easier for slower hardware to implement as it requires less processing.
In HD
production, the HD-SDI interface supports the 24p framerate in addition to the 60i and 50i framerates. Many HD monitors are able to receive a 24p signal (not a 60i signal with pulldown added) and can display the 24p material directly.
For end-user viewing of HD material, many digital formats are offering 24p support. Computer formats such as Windows Media, Quicktime, and Real video can play 24p video directly on a computer monitor.
s, however, are capable of storing the native 24p frames. Every Hollywood movie is laid to disc as a 24p (actually 23.976p – see below) stream. With a progressive-scan DVD player and a progressive display, such as an HDTV, only the progressive frames are displayed and there is no conversion to an interlaced format – eliminating the appearance of any interlace or de-interlacing artifacts. When displayed on a standard NTSC TV (which only displays 60i) the DVD player will add 3:2 pulldown to the signal.
In traditional television broadcast and VHS, the video stream has 3:2 pulldown added. This material cannot be displayed progressively without the resolution loss of de-interlacing, unless the de-interlacer has accurate cadence detection.
and digital cinema
such as the Star Wars prequel trilogy.
In 2002, Panasonic released the Prosumer
DV
camera AG-DVX100 (followed by the updated models AG-DVX100A in 2003 and AG-DVX100B in 2005). This camera was the first DV camera that could switch between different frame rates, including 60i, 30p, and 24p with a choice between the 2:3:3:2 or 3:2 pulldown schemes. The 24p feature on the camera produces film-like video that is preferred by many narrative filmmakers. Canon
soon followed suit with the Canon XL-2, offering the same frame rates and pulldown choices as the DVX100.
Following the success of the DVX100, in December, 2005, Panasonic released the Panasonic AG-HVX200, which offers 24p HD
at the sub-$10,000 level. Basically an HD version of the DVX100 series, it heavily targets independent filmmakers, as HD has a much higher resolution than DV and will generally look superior on a film blow-up. It is also noteworthy that the camera records HD footage, complete with clip information, to static P2
memory cards instead of tape. This could potentially signify a radical change in the video editing workflow.
For recording 24p to tape in formats which typically do not support 24p, such as DV, options include PsF
, 2:3 Pulldown
and advanced pulldown.
Some music video
s and television series today are shot with 24p video.
Film productions may be shot at exactly 24.000 frame/s. This can be a source of confusion and technical difficulties if material is treated as normal video, since the slightly differing framerates can be problematic for video and audio sync. However, this is not a problem if the video material is merely treated as a carrier for material which is known by the editing system to be "true" 24frame/s, and audio is recorded separately from moving images, as is normal film practice.
and Blu-ray Disc
support the 24p frame rate, but technical implementations of this mode are different among the two formats. Blu-ray Disc
supports 24p with its native timing, while HD DVD
uses 60i timing for 24p (replacing missing frames with "repeat field flags").
Increasingly, however, non-tape-based video systems are making use of native 24 frame/s formats, reducing this complication.
In general, 24 frames-per-second video has more trouble with fast motion than other, higher frame rates, sometimes showing a "strobe" or "choppy" motion, just like 24 frame/s film will if shot as if it's video, without careful panning, zooming, and slower camera motion. It is therefore not well-suited for programming requiring spontaneous action or "reality" camerawork. 24p can also hurt the credibility of newscasts by making news footage look too much like staged movie clips – though many newscasts do incorporate 24p footage.
It should also be noted that while the strobe of 24p is in many ways considered a disadvantage, it's also part of the "film look." 24 frame/s film strobes in exactly the same way.
Most consumer-level video editors (particularly non-HD ones) are designed for 60 frames per second interlaced video that displays on a television. Video produced natively at 60i displays properly on televisions and can be properly de-interlaced to a quality 30p by most hardware and software in LCD and Plasma television sets, in addition to being suitable for viewing on a computer screen. Working with 24p video for non-film viewing adds new and challenging implementation considerations.
The addition of 24p is sometimes awkwardly implemented. Incorrect user settings can result in a 24p frame at the edge of an edit existing on only one NTSC field, thus cutting its resolution in half. If a non-linear editor is incapable of removing pulldown, the standard 3:2 pulldown pattern should be used when shooting.
The production of 24p video that plays on a television at 60 Hz will not be exactly the same as theater film look. It may have some strobe or 'film effect' but lacks the proper film production and film screen viewing.
Most professional video cameras record the best quality at 60i before they output 24p video in their output settings. They do this so that their sensors and software can be calibrated for standard video use and yet the user can still achieve the 24p look.
equipment is being designed to also handle the 48p frame rate along with the traditional 24p. 48p has twice the (video-like) motion (temporal resolution
) of 24p, but also requires more bandwidth
, data storage
, and potentially illumination level. Peter Jackson's two part film The Hobbit is one of the upcoming productions which will make use of the 48p frame rate .
Some current, best-of-breed professional video cameras provide 120 frame/s progressive capture, which is 5 times 24p and can be converted to 24p, 30p, 50i, and 60i/p with editing options and precision in motion shots.
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
frame rates) frame rate with progressive scan
Progressive scan
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...
ning (not interlaced). Originally, 24p was used in the non-linear editing of film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
-originated material. Today, 24p formats are being increasingly used for aesthetic reasons in image acquisition, delivering film-like motion characteristics. Some vendors advertise 24p products as a cheaper alternative to film acquisition.
When working entirely within the digital non-linear domain, 24p material is more easily handled than material of higher frame rates. 24p material requires care when it is processed using equipment designed for standard video frame rates.
There are two common workflow
Workflow
A workflow consists of a sequence of connected steps. It is a depiction of a sequence of operations, declared as work of a person, a group of persons, an organization of staff, or one or more simple or complex mechanisms. Workflow may be seen as any abstraction of real work...
s for processing 24p material using video equipment, one using PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
frame rates, and the other using NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
frame rates. Of these two, the PAL route is the simpler, but each has its own complications.
Converting 24p to PAL
24p material can be converted to the PALPAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
format with the same methods used to convert film to PAL. The most popular method is to speed up the material by 25/24 (4%). Each 24p frame will take the place of two 50i
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
fields
Field (video)
In video, a field is one of the many still images which are displayed sequentially to create the impression of motion on the screen. Two fields comprise one video frame...
. This method incurs no motion artifacts
Artifact (error)
In natural science and signal processing, an artifact is any error in the perception or representation of any visual or aural information introduced by the involved equipment or technique....
other than the slightly increased speed, which is typically not noticeable. As for audio, the ~4% increase in speed raises the pitch
Pitch (music)
Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale.Pitches are compared as "higher" and "lower" in the sense associated with musical melodies,...
by 0.7 of a semitone
Semitone
A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically....
, which again typically is not noticed. Sometimes the audio is pitch shifted
Audio timescale-pitch modification
Time stretching is the process of changing the speed or duration of an audio signal without affecting its pitch.Pitch scaling or pitch shifting is the opposite: the process of changing the pitch without affecting the speed...
to restore the original pitch.
If 24p footage cannot be sped up, (for example if it were coming through a live NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
or HD
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...
feed
Signalling (telecommunications)
In telecommunication, signaling has the following meanings:*the use of signals for controlling communications...
) it instead can be converted in a pattern
Pattern
A pattern, from the French patron, is a type of theme of recurring events or objects, sometimes referred to as elements of a set of objects.These elements repeat in a predictable manner...
where most frames were held on screen for two fields, but every half second a frame would be held for three fields. Thus the viewer would see motion stutter twice per second. This was the common result when programs were shot on film or had film portions, edited on NTSC, and then shown in PAL countries (mostly music video
Music video
A music video or song video is a short film integrating a song and imagery, produced for promotional or artistic purposes. Modern music videos are primarily made and used as a marketing device intended to promote the sale of music recordings...
s). NTSC to PAL conversion also tends to blur
Motion blur
Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure.- Photography :When a camera...
each film frame into the next, and so is seen as a sub-optimal way to view film footage.
30p
Progressive scan
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...
can be preferable over 24p since performing a standards conversion to 25i PAL has fewer technical complexities - any NTSC-PAL converter
Television standards conversion
Television standards conversion is the process of changing one type of TV system to another. The most common is from NTSC to PAL or the other way around. This is done so TV programs in one nation may be viewed in a nation with a different standard...
will do. The larger differences between the 30p and 25i framerates will cause less noticeable motion artifacts upon conversion.
Non-linear editing and 24/25 telecine
The process of transferring 24frame/s video at 25frame/s rates is also the most common method for ingesting 24p film rushes into a non-linear editor. The resulting 25frame/s video can then be transferred into a non-linear editing system at 25 frame/s, maintaining the 1:1 frame correspondence between film frames and video frames. Once in the non-linear editing system, the editing system, knowing that the material actually originated 24frame/s rather than at 25frame/s, will replay it at the correct speed.The original film Keykode
Keykode
KeyKode is an Eastman Kodak Company advancement on edge numbers, which are letters, numbers and symbols placed at regular intervals along the edge of 35 mm and 16 mm film to allow for frame-by-frame specific identification...
and 24frame/s audio timecode can be then be reconciled with the 25frame/s telecine timecode by the generation of a telecine log file containing this information. Again, once the non-linear editor has this information, editing can be performed entirely in terms of 24frame/s timecode, and the Keykode information preserved for either film cutting or digital intermediate
Digital intermediate
Digital intermediate is a motion picture finishing process which classically involves digitizing a motion picture and manipulating the color and other image characteristics. It often replaces or augments the photochemical timing process and is usually the final creative adjustment to a movie...
post-production of scanned film images.
Because sound is recorded separately from moving pictures in 24p projects, there are no problems regarding synchronization or audio pitch: the audio material is simply ingested separately from the moving picture material at its natural rate, and synchronized within the non-linear editor.
Conversion of 24p to NTSC-based frame/field rates
Working with 24p material via video equipment working at NTSC frame rates has many of the same attributes as the 24frame/s workflow, but is more complicated by the NTSC-rate practice of using telecine pull-down rather than the PAL practice of transferring 24frame/s material at 25frame/s.At standard analog NTSC video rates (29.97 frames per second) a full "interlaced" frame, unlike a progressive frame, is nearly 1/30th of a second and is composed of two separate "fields," each field nearly 1/60 second. The first field (the odd field) contains visible scan lines 21-263 and the second field (the even field) contains visible scan lines 283-525. What is seen onscreen is two of these fields, "interlaced" together, to produce a single full frame. This comes from the proper longhand designation being vertical resolution, followed by the interlaced/progressive notation, and then the frame rate. So typical DV video is correctly listed as 480i/30. The long hand for 24p is 480p/24. Often the resolution is dropped and the i/p designation moved after the frame rate for shorthand.
24p cameras do not, as NTSC video cameras do, shoot 30 interlaced frames per second (60 fields); they shoot 24 full progressive frames per second.
24p material can be recorded directly into formats that support the framerate. Some of the emerging HD formats support the 24p framerate in addition to 60i and 50i (PAL). Previously, few formats supported 24p and the industry used workarounds to work with 24p footage with 60i equipment.
To record 24p material onto a 60i format (i.e. any NTSC-based format), pulldown is typically added to 'pad' the 24 frames into 60 fields. This is done by taking every frame and splitting it into two fields. Then, every second frame has one of its fields duplicated, resulting in three fields. The fields are then played back in that pattern – 2-3-2-3-2-3-2-3-2-3-2-3-2-3 … and so on. The resulting video becomes a 60i stream and can be displayed on NTSC monitors. However, the aesthetic of 24p motion is retained and the footage does not have the motion of typical 60i video.
This 3:2 pulldown is the same process that is used when transferring film into video
Telecine
Telecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
.
Any editing application which supports NTSC video can be used to edit footage employing the 3:2 pulldown scheme. It can be captured as a standard 60i file and edited like footage from any other camera, while still retaining its 24p aesthetic. There can be issues when editing the footage as 60i, however, including choppiness in short transitions or fades, and also a mismatch in the motion characteristics of the footage and any graphics which may be added to it, such as text or logos. So, while 24p footage can be edited as 60i, it is usually better to edit the footage on a 24p timeline with the pulldown removed.
Most current prosumer-level editing applications which edit native 24p can remove the 3:2 pulldown for editing in native 24p, although some cannot. However, this is not ideal; the removal of the 3:2 pulldown involves reconstruction of every fourth frame from two different field groups, which can cause a generational loss and some banding problems if the application doesn't interpret the footage properly. Therefore, using the 3:2 pulldown scheme is not ideal when planning to edit on a 24p timeline.
Note: "3:2 pulldown" has a cadence of 2-3-2-3-2-3..., but in the industry is called "3:2 pulldown", even though the cadence is 2-3. Some people use the term "2:3 pulldown", which corresponds to the cadence, but is not normally used in the industry for the technique.
Advanced pulldown
Another pulldown pattern is the "advanced pulldown" ("24pA") pattern, first implemented in the Panasonic AG-DVX100Panasonic AG-DVX100
The Panasonic AG-DVX100 was the first affordable digital progressive scan camcorder.The camera is popular among television studios and is popular with independent film makers because of its many film-emulating features and has a large following. Currently the latest and last revision is the DVX102B...
camcorder. Instead of padding the frames into a repeating 3:2 pattern, the frames are padded into a 2:3:3:2 pattern. This pattern is specific to the NTSC DV format, and would serve no purpose in native 24p formats.
It converts the first frame into two fields, the second into three fields, the third into three fields, and the fourth into two fields. It then repeats this pattern for every group of four frames that follows. This pulldown pattern is used to avoid segmenting a 24p frame into two different 60i fields that exist in two different 60i frames. When a 24p frame is split up and recorded into separate 60i fields, interlacing artifacts can exist in the 60i "frames" (i.e. two fields). These artifacts decrease the compression efficiency of DV
DV
DV is a format for the digital recording and playing back of digital video. The DV codec was launched in 1995 with joint efforts of leading producers of video camcorders....
and can result in cycles of efficient compression followed by less-efficient compression. The advanced pulldown scheme avoids this as every 24p frame can be found intact within the resulting sequence of 60i frames, yet the compression efficiency remains the same as with 3:2 pulldown.
When editing 24pA footage, conversion from 60i back to the original 24p is very efficient. It only requires blending the fields made from the frames back into full frames. Then, only every fifth frame will be made up of fields from two different frames, and that frame can be discarded, leaving only the other four full frames. In order for this to work properly, the DVX100 camera records video in chunks of five video frames. This ensures that each clip has regular and predictable cadence.
Because the 2:3:3:2 scheme was devised for efficient pulldown removal for editing, and because 24p editing applications more universally support its removal, it should always be used when planning to edit in native 24p.
Editing systems need specific support for the 24pA format to be able to detect and remove the pulldown properly so that the 24p frames can be edited in a 24p timeline. Many but not all prosumer and professional-level non-linear editing systems are able to recognize and remove this advanced pulldown scheme. However, among the editing applications able to remove pulldown and edit in native 24p, it is more common for them to have support for 24pA 2:3:3:2 pulldown than for standard 24p 3:2 pulldown removal.
Still other editing applications have the option for editing on a 24p timeline, and will accept footage where the pulldown has already been removed in another application.
Remember that although computer editing systems may refer to "24p", usually the precise frame rate is 23.976 frame/s. To add to confusion, the popular editing program Final Cut Pro refers to 23.976 as "23.98" in menus and dialogs, even though it correctly works with the footage at the 23.976 frame rate.
Also because the 2:3:3:2 pulldown scheme was devised in order to make pulldown removal for editing in native 24p more efficient, the pulldown arrangement is not ideal for watching footage. There can be exaggerated stutters in motion, because the frames which are split into three fields are not only onscreen for 50% longer than the other frames, they are back-to-back. As such, 2:3:3:2 pulldown should be used only when a native 24p edit is planned, and not for final viewing. This includes when shooting the footage initially, and also when printing back to tape from an NLE.
Diagram here
60i to 24p conversions
Another method of achieving the 24p aesthetic is to capture 60i footage and convert it into 24p. Various techniques can be used to perform this conversion. A simple scheme would blend the fields together. This can result in motion artifacts where comb-like jagged artifacts appear in areas of high motion. De-interlacingDeinterlacing
Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
can remove these artifacts, but certain methods will cause up to half the footage's vertical resolution to be lost. Adaptive de-interlacing schemes only de-interlace areas of high motion, hence preserving resolution in stationary areas. More advanced techniques can be used to mitigate problems such as aliasing from the temporal displacement between the 60i fields.
The Optical Flow Method
This is currently the highest quality method of converting 60i footage to 24p. It involves using optical flowOptical flow
Optical flow or optic flow is the pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer and the scene. The concept of optical flow was first studied in the 1940s and ultimately published by American psychologist James J....
to extrapolate 24 frames of information from 60 frames while compensating for the time displacement between the two. For example, in one second of 60i footage, each image is captured at 1/60 second, which does not perfectly align with images that would have been captured 24 times per second. Simply "cherry picking" 24 images out of 60 does not present 24 frames with perfect temporal consistency, since more or less time may have elapsed between frames. The result is a slightly jittery picture, which appears to jitter in a cyclic fashion. Optical flow algorithms will analyze the footage and make corrections to the picture in order to better "fit" each frame into the new 24 frame sequence. The resulting footage is much smoother because it simulates equal exposure time between frames.
For best results, footage should be deinterlaced and frame-doubled to 60p. This preserves all of the footage's temporal information, which is key in determining what the "missing" points in time should look like when converting to 24 frame/s.
The last step is to compensate for the lack of motion blur
Motion blur
Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure.- Photography :When a camera...
in the 60i footage. Since the images were captured at 1/60 second, there is less motion blur between images than there would have been if shot at 24 frame/s with a 180° shutter (i.e. 1/48 second exposure time). Optical flow is used to introduce motion blur between frames, mimicking the motion blur present when shooting the standard 180° shutter angle. This method of creating motion blur is far more realistic than simple frame blending, which is simple to implement and usually a standard feature in most non-linear editing programs.
The optical flow method also works with 30p footage and is currently the best option for 30p to 24p conversion.
Using Adobe After Effects
This method requires the use of Adobe After Effects and applies to any interlaced material. It uses all of the temporal information in 50i or 60i footage to create the equivalent of a slow motion sequence shot at 50 or 60 frames per second, respectively. It also does not require multiple render passes to achieve the effect, avoiding generation loss from multiple compression cycles.Using VirtualDub + AviSynth
VirtualDub, along with AviSynth, can be used to perform a 60i to 24p conversion in a similar way to After Effects. AviSynth performs the deinterlacing, then frameservesFrameserver
A frameserver is a computer program that streams video to another program, called a frameclient, using a process known as frameserving. The video is sent directly to the frameclient, frame by frame...
the 60p half-resolution result to VirtualDub for further processing (specifically, adjusting field height using the "field bob" filter, resizing back to full resolution and then outputting at 24 frame/s). The reason AviSynth must be used is because VirtualDub cannot split the fields into a 60p sequence on its own, and this technique requires 60p input.
Displaying 24p material
With NTSC equipment, it is impossible to display a 24p signal directly as the monitors only support the 60i framerate. Hence, pulldown must be added to the 24p material to be displayed. Most editing systems will either add 3:2 pulldown or 2:2:2:4 pulldown. In the 2:2:2:4 pulldown scheme, used as a choice primarily by Apple's Final Cut ProFinal Cut Pro
Final Cut Pro is a non-linear video editing software developed by Macromedia Inc. and then Apple Inc. The most recent version, Final Cut Pro X, runs on Mac personal computers powered by Mac OS X version 10.6.7 or later and using Intel processors...
, every fourth frame is repeated. This scheme is easier for slower hardware to implement as it requires less processing.
In HD
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...
production, the HD-SDI interface supports the 24p framerate in addition to the 60i and 50i framerates. Many HD monitors are able to receive a 24p signal (not a 60i signal with pulldown added) and can display the 24p material directly.
For end-user viewing of HD material, many digital formats are offering 24p support. Computer formats such as Windows Media, Quicktime, and Real video can play 24p video directly on a computer monitor.
24p compared to 30p
As Charles Poynton explains, the 24 frame/s rate is not just a cinema standard, it is also "uniquely suited to conversion to both 50 Hz systems (through 2:2 pulldown, 4% fast) and 59.94 Hz systems (through 2:3 pulldown, 0.1% slow). Choosing a rate other than 24 frame/s would compromise this widely accepted method of conversion, and make it difficult for film producers to access international markets".24p on DVD
DVDDVD-Video
DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder...
s, however, are capable of storing the native 24p frames. Every Hollywood movie is laid to disc as a 24p (actually 23.976p – see below) stream. With a progressive-scan DVD player and a progressive display, such as an HDTV, only the progressive frames are displayed and there is no conversion to an interlaced format – eliminating the appearance of any interlace or de-interlacing artifacts. When displayed on a standard NTSC TV (which only displays 60i) the DVD player will add 3:2 pulldown to the signal.
In traditional television broadcast and VHS, the video stream has 3:2 pulldown added. This material cannot be displayed progressively without the resolution loss of de-interlacing, unless the de-interlacer has accurate cadence detection.
24p video production
Increasingly, 24p is used to acquire video. The most prolific use of this has been with HDTVHigh-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
and digital cinema
Digital cinema
Digital cinema refers to the use of digital technology to distribute and project motion pictures. A movie can be distributed via hard drives, optical disks or satellite and projected using a digital projector instead of a conventional film projector...
such as the Star Wars prequel trilogy.
In 2002, Panasonic released the Prosumer
Prosumer
Prosumer is a portmanteau formed by contracting either the word professional or less often, producer with the word consumer. For example, a prosumer grade digital camera is a "cross" between consumer grade and professional grade...
DV
DV
DV is a format for the digital recording and playing back of digital video. The DV codec was launched in 1995 with joint efforts of leading producers of video camcorders....
camera AG-DVX100 (followed by the updated models AG-DVX100A in 2003 and AG-DVX100B in 2005). This camera was the first DV camera that could switch between different frame rates, including 60i, 30p, and 24p with a choice between the 2:3:3:2 or 3:2 pulldown schemes. The 24p feature on the camera produces film-like video that is preferred by many narrative filmmakers. Canon
Canon Inc.
is a Japanese multinational corporation that specialises in the manufacture of imaging and optical products, including cameras, camcorders, photocopiers, steppers and computer printers. Its headquarters are located in Ōta, Tokyo, Japan.-Origins:...
soon followed suit with the Canon XL-2, offering the same frame rates and pulldown choices as the DVX100.
Following the success of the DVX100, in December, 2005, Panasonic released the Panasonic AG-HVX200, which offers 24p HD
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...
at the sub-$10,000 level. Basically an HD version of the DVX100 series, it heavily targets independent filmmakers, as HD has a much higher resolution than DV and will generally look superior on a film blow-up. It is also noteworthy that the camera records HD footage, complete with clip information, to static P2
P2 (storage media)
P2 is a professional digital recording solid-state memory storage media format introduced by Panasonic in 2004, and especially tailored to electronic news-gathering applications. It features tapeless recording of DV, DVCPRO, DVCPRO25, DVCPRO50, DVCPRO-HD, or AVC-Intra streams on a solid-state...
memory cards instead of tape. This could potentially signify a radical change in the video editing workflow.
For recording 24p to tape in formats which typically do not support 24p, such as DV, options include PsF
Progressive segmented Frame
Progressive segmented Frame is a scheme designed to acquire, store, modify, and distribute progressive-scan video using interlaced equipment and media....
, 2:3 Pulldown
Telecine
Telecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
and advanced pulldown.
Some music video
Music video
A music video or song video is a short film integrating a song and imagery, produced for promotional or artistic purposes. Modern music videos are primarily made and used as a marketing device intended to promote the sale of music recordings...
s and television series today are shot with 24p video.
23.976p
Many 24p productions, especially those that are made only for TV and video distribution, actually have a frame rate of 24 * 29.97 / 30 frame/s, or 23.976frame/s (24/1.001 to be exact). Many use the term "24p" as a shorthand for this frame rate, since "23.976" does not roll off the tongue as easily. This is because the "30frame/s" framerate of NTSC is actually 30/100.1%, also referred to as 29.97frame/s – this framerate is matched when video at 23.976frame/s has a 3:2 pulldown applied. Similarly, 60i is shorthand for 60/100.1% fields per second.Film productions may be shot at exactly 24.000 frame/s. This can be a source of confusion and technical difficulties if material is treated as normal video, since the slightly differing framerates can be problematic for video and audio sync. However, this is not a problem if the video material is merely treated as a carrier for material which is known by the editing system to be "true" 24frame/s, and audio is recorded separately from moving images, as is normal film practice.
24p in high definition disc formats
Both HD DVDHD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
and Blu-ray Disc
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
support the 24p frame rate, but technical implementations of this mode are different among the two formats. Blu-ray Disc
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
supports 24p with its native timing, while HD DVD
HD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
uses 60i timing for 24p (replacing missing frames with "repeat field flags").
Disadvantages of 24p
24p and 24pA, notably when related to SD/DV video, introduce an increasingly complicated and esoteric technical complexity to video editing which does not exist at NTSC's native 30p/60i. Camera settings, file interpretation settings, program settings, sequence/timeline settings and export settings must be calibrated by the user, oftentimes manually, in order to preserve image information and motion registration. Because of the sometimes inconsistent shorthand and terminology employed amongst vendors who implement the technology, as well as the subtle practical effects the various settings have on video playback, 24p is often considered a needlessly complicated transitory technology, which serves only as a bridge to true, native 24 frame/s digital film.Increasingly, however, non-tape-based video systems are making use of native 24 frame/s formats, reducing this complication.
In general, 24 frames-per-second video has more trouble with fast motion than other, higher frame rates, sometimes showing a "strobe" or "choppy" motion, just like 24 frame/s film will if shot as if it's video, without careful panning, zooming, and slower camera motion. It is therefore not well-suited for programming requiring spontaneous action or "reality" camerawork. 24p can also hurt the credibility of newscasts by making news footage look too much like staged movie clips – though many newscasts do incorporate 24p footage.
It should also be noted that while the strobe of 24p is in many ways considered a disadvantage, it's also part of the "film look." 24 frame/s film strobes in exactly the same way.
Most consumer-level video editors (particularly non-HD ones) are designed for 60 frames per second interlaced video that displays on a television. Video produced natively at 60i displays properly on televisions and can be properly de-interlaced to a quality 30p by most hardware and software in LCD and Plasma television sets, in addition to being suitable for viewing on a computer screen. Working with 24p video for non-film viewing adds new and challenging implementation considerations.
The addition of 24p is sometimes awkwardly implemented. Incorrect user settings can result in a 24p frame at the edge of an edit existing on only one NTSC field, thus cutting its resolution in half. If a non-linear editor is incapable of removing pulldown, the standard 3:2 pulldown pattern should be used when shooting.
The User Experience
It is worth noting that almost all 24p video produced will be eventually converted to 50 Hz or 60 Hz playback when viewed on a computer or television with the exception of conventional CRT monitors and new HD televisions that natively support multiples of 24 Hz. CRTs can display images at many different refresh rates. New TVs scan and display images at 50 Hz or 60 Hz and then will add their own conversion algorithms.The production of 24p video that plays on a television at 60 Hz will not be exactly the same as theater film look. It may have some strobe or 'film effect' but lacks the proper film production and film screen viewing.
Most professional video cameras record the best quality at 60i before they output 24p video in their output settings. They do this so that their sensors and software can be calibrated for standard video use and yet the user can still achieve the 24p look.
Future
Next generation digital cinemaDigital cinema
Digital cinema refers to the use of digital technology to distribute and project motion pictures. A movie can be distributed via hard drives, optical disks or satellite and projected using a digital projector instead of a conventional film projector...
equipment is being designed to also handle the 48p frame rate along with the traditional 24p. 48p has twice the (video-like) motion (temporal resolution
Temporal resolution
Temporal resolution refers to the precision of a measurement with respect to time. Often there is a tradeoff between temporal resolution of a measurement and its spatial resolution. This trade-off can be attributed to the finite speed of light and the fact that it takes a certain period of time...
) of 24p, but also requires more bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
, data storage
Data storage device
thumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
, and potentially illumination level. Peter Jackson's two part film The Hobbit is one of the upcoming productions which will make use of the 48p frame rate .
Some current, best-of-breed professional video cameras provide 120 frame/s progressive capture, which is 5 times 24p and can be converted to 24p, 30p, 50i, and 60i/p with editing options and precision in motion shots.
See also
- Frame rateFrame rateFrame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
- TelecineTelecineTelecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
- FilmizingFilmizingFilmizing is a process that makes video productions seem to have been shot on film. The term is generic and informal. The process is usually electronic, although filmizing can sometimes occur as an un-intentional by-product of some optical techniques, such as telerecording.-Differences between...
(a.k.a. Filmlook) - Progressive scanProgressive scanProgressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...