24p
In video technology, 24p refers to a video format that operates at 24 frames per second frame rate with progressive scanning. 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 workflows 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.
24p vs. PAL video
Converting 24p to PAL
24p material can be converted to the PAL format with the same methods used to convert film to PAL. The most popular method is to speed up the material by 1/24. 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 ≈4.1% increase in speed raises the pitch by 0.707 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, 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. 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.
Non-linear editing and 24/25 telecine
The process of transferring 24 frame/s video at 25 frame/s rates is also the most common method for ingesting 24p film rushes into a non-linear editor. The resulting 25 frame/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 24 frame/s rather than at 25 frame/s, will replay it at the correct speed.The original film Keykode and 24 frame/s audio timecode can be then be reconciled with the 25 frame/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 24 frame/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.
24p vs. NTSC video
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 24 frame/s workflow, but is more complicated by the NTSC-rate practice of using telecine pull-down rather than the PAL practice of transferring 24 frame/s material at 25 frame/s.At 525 lines analog NTSC video rates 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 contains visible scan lines 21-263 and the second 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 ; they shoot 24 full progressive frames per second.
24p material can be recorded directly into formats that support the framerate. Some of high definition formats support the 24p framerate in addition to 60i and 50i. 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, 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.
Advanced pulldown
Another pulldown pattern is the "advanced pulldown" pattern, first implemented in the Panasonic AG-DVX100 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". 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 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. 23.976 is also not precise though, as the real frame rate is 24000 ÷ 1001, so 23.98 is also a correct approximation.
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.