24p

24p is a video format which runs twenty-four progressive (hence the "P") frames per second, essentially the same as film does. Originally used for utilitarian purposes in non-linear editing, today the format is widely used for aesthetic reasons by both high-end professional and independent media makers. In particular, 24P HD already provides a reasonably viable alternative to the film format and may replace it altogether in the future.

At standard analog NTSC video rates (30/second) a full "interlaced" frame, unlike a progressive frame, is 1/30th of a second and is composed of two separate "fields," each 1/60 per second. The first field containing the odd horizontal scan lines and the second, the even lines. What is seen onscreen is two of these fields, "interlaced" together, to produce a single full 1/30th per second frame.(The commonly stated 30 frames/second is a simplification. The actual frame rate is 29.97/second. To deal with this desparity one frame is dropped every ten minutes.)

Conversion to 24P involves removing certain frames of the video (which will start for example at 60 fields interlaced per second or 60i) and staggering the remaining footage together to end up with 24 full images that show in sequence, or "progression." This is, of course, a digital process and usable only with digital video equipment. The process is known as a "pulldown."

Older, analog NTSC video must still have everything converted (up or down) to 30 interlaced frames, so the resulting footage is for most purposes still just video, either on the NTSC or PAL standard and Standard Definition (SD) or High Definition (HD). Of course this video signal, and almost any television set, is still interlaced-- what you are getting with 24P is a sort of "simulated" progressive medium, the same thing that you are getting in any DVD, VHS or television broadcast of a Hollywood film.

24p was originally developed for non-linear editing systems such as Avid to create a frame-for-frame correlation between film and digitized video, in order to achieve the most accurate editing possible. But it began to be applied to footage originally acquired on video, along with other post-production effcts, to create a film-like effect.

Increasingly, 24p is used to acquire video. In these cases a camera does an "on-board pulldown" as it shoots. The most prolific use of this has been with HDTV and digital cinema. Cameras such as the Panasonic AJ-SDX900 have been heavily used in TV and film work, and the Star Wars Prequels were shot on a very high-end digital 24P HD cameras. 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 can switch between different frame rates. The 24P feature on the camera produces film-like video generally agreed to be preferable to normal DV, especially for narrative filmmakers. Canon soon followed suit with the XL2. Although resembling film look in color and motion, the resolution of 24P DV is no higher than regular video-- a point of confusion for many film and video makers.

Following the success of the DVX100, in December 2005 Panasonic released the Panasonic AG-HVX200, which will offer true HD, 24P capacity at the prosumer level. Basically an HD version of the DVX100A, it will heavily target 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 will record 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, 3:2 Pulldown, advanced pulldown, and 24-over-60.

Disadvantages

In duplicating the look of film, 24p also inherits some of film's disadvantages. By definition, 24p video is incapable of high motion, and is therefore not well suited for sports, home movies, or programing requiring spontaneous action or handheld camerawork. 24p can also hurt the credibility of newscasts by making news footage look too much like staged movie clips.

Most video editors (particularly non-HD ones) are designed for 30 frames per second, and 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.

Most seriously, 24p is very unpopular in nations using PAL or SECAM video. (This includes most of Eurasia, Africa, Australia and South America.) The reason is that converting 24p to PAL's 50 hz scan rate would require 2 frames in each second of video to be held for 3 video fields instead of two. The viewer would thus see motion stutter twice per second. To avoid this, American movies and 24p video are usually sped up to 25 hz for viewing - but this can create audio problems and is impossible for live broadcasts. (Ironically NTSC nations have no motion problems with either 24 hz or Europe's 25 hz.)

See also

• 60i

External links

• 24 Questions about DV 24 Frame Progressive