Standard-Definition Standards

Despite the variations, there are only two fundamental video standards you'll encounter in the standard-definition production universe, as outlined in the following sections.

525/59.94, a.k.a "NTSC"

Video in North America, Japan, and South Korea is based on the NTSC (National Television Standards Committee) broadcast standard. Although NTSC refers to a specific manner of encoding a composite video signal with subcarrier-modulated color, it's often used as shorthand for all the video formats that conform to NTSC's standards for timing, frequency, frame rate, and line count.

Frame Rate and Scanning

NTSC video has a frame rate of 30 Hz x 1000 ÷ 1001, normally abbreviated as 29.97 Hz. A 2:1 interlace is used, resulting in two fields per frame. The field rate is 60 Hz x 1000 ÷ 1001, or approximately 59.94 Hz. The line rate (frequency of horizontal scanning) is 15,750 Hz x 1000 ÷ 1001, or about 15.734 Hz.

Note

That annoying high-pitched whine that TV monitors make? That's the sound of the line rate, sitting right in the upper reaches of human hearing. The high-voltage amplifiers deflecting the electron beam in a CRT cause enough vibration for you to hear the whine.

Frame Size and Aspect Ratio

NTSC uses a 4x3 aspect ratio frame with 525 scanlines per frame. Of these, about 483 contain active picture content, and the rest are used for vertical blanking and sync.

When digitized to ITU-R BT.601 specifications, the active picture area is 704 pixels wide and 486 pixels tall. Some digital production tools use all 720 pixels per scanline for active picture content.

Signal Levels

Peak to peak signal: 1 volt, or 140 IRE units total.

100% white: 714 millivolts, or 100 IRE units.

Sync tip: 286 millivolts, or 40 IRE units.

In North America, NTSC composite black is at 54 millivolts, or 7.5 IRE. Outside North America, and in component digital and most component analog systems, black is at 0 millivolts, or 0 IRE.

Subcarrier Frequency

Color is subcarrier-modulated at 3.58 MHz in the composite signal.

Variations

Some parts of the world use NTSC timing and frame sizes but modulate color at the PAL subcarrier rate of 4.43 MHz. If an NTSC-4.43 tape is played back in NTSC-3.58 equipment, or vice versa, you'll see a monochrome picture.

NTSC-format DV records only 480 scanlines, not 486. When a DV frame is placed into 486-line raster, 4 blank lines are added to the top of the picture and 2 at the bottom.

24 fps material is normally carried in NTSC using a 2:3 pulldown, although the 2:3:3:2 pulldown is becoming more common for standard-definition digital cinematography. In all cases the 24p material is really shot (or transferred from film) at 23.98 fps and carried in a standard 29.97 fps signal.

30p captures 29.97 frames per second, breaking the frames into two fields for recording. (The "Frame Movie Mode" on some Canon and Panasonic camcorders is a form of 30p.)

There are also systems (like JVC's HDV cameras and Panasonic's DVCPRO-Progressive system) that shoot a full 480-line, 60 frame per second picture, but FCP doesn't currently support these systems.

625/50, a.k.a. "PAL"

PAL, or Phase Alternating Line, is a German-designed broadcast standard now used through most of the rest of world. PAL replaced several incompatible monochrome standards (such as the UK's 405-line broadcasts and France's 819-line television) and is now the basis for all standard-definition video that isn't NTSC-based.

Frame Rate and Scanning

PAL uses 25 frames per second with a 2:1 interlace, thus 50 fields per second. The line rate is 15,625 Hz.

Frame Size and Aspect Ratio

PAL's pictures have a 4x3 aspect ratio. There are 625 scanlines total, of which 576 are active. PAL, when digitized, also fits into a 720-pixel scanline.

Note

PAL has 20 percent fewer frames per second than NTSC, but each frame has 20 percent more scanlines. When digitized to 601 specifications, both standards require the same number of bits per second.

Signal Levels

Peak to peak signal: 1 volt. IRE units are not used in PAL measurement.

100% white: 700 millivolts.

Sync tip: 300 millivolts.

Subcarrier Frequency

Color is subcarrier-modulated at 4.43 MHz in the composite signal.

Variations

SECAM, Système Èlectronique Couleur Avec Memoire (sequential color with memory), is a transmission standard developed by the French, and used in France, Russia, and various countries in Europe and Africa where those two countries once held sway. SECAM is used for over-the-air transmission only; all the production equipment is PAL-based.

Note

Some wags state that SECAM stands for System Essentially Contrary to the American Method, but sadly there is no similar jocular derivation of the PAL acronym.

A fair bit of content in the PAL/SECAM world is now 16x9 widescreen material. A signal in the vertical interval triggers compatible TV sets to modify their scanning to show the program in its proper aspect ratio.

24 fps material is sped up 4 percent to 25 fps and transferred using, in effect, a 2:2 pulldown; film shot for television is often shot at 25 fps to begin with. Each frame of film transfers to two fields of video.

25p production cameras are becoming common for digital cinematography in the PAL world. 25p captures 25 full frames per second, breaking the frames into two fields for recording. (The "Frame Movie Mode" on some Canon and Panasonic camcorders is a form of 25p.)