by July 4, 2002 0 comments



Format in the context of video can .mean many things–the format of the tape on which video is recorded for professional broadcasting, the format your camcorder uses, the format in which your TV signal is encoded, or the format of the screen in which you see video. We look at these areas in the video terrain.

In the studios
In India, most studios and TV channels use betacam (beta) or digital betacam (digibeta)–both Sony’s formats. Generally, a higher tape width, more data transfer per second and lower compression ratio, make for better quality video. However, these also add to cost, because you use more tape and need more resources to work with the video. 

See the table on the right-hand page for the most commonly used of these formats.

Camcorders at Home
The most known digital format here is DV or MiniDV with Digital 8 not far behind. There are several analog recorders and formats doing the rounds too. 

DV. Beginning its journey as the format of choice on digital camcorders for the home, DV is making a transition into newsrooms and TV channels. Several professional formats–DVCAM, DVC PRO and DVC PRO 50–have sprung from it. The one drawback of DV is that sometimes audio doesn’t synchronize too well with video while editing. This, however, is not the case with its professional cousins. The tapes on which DV is recorded in home equipment are called MiniDV tapes. These are really small, as the tape is only 6.35 mm or ¼” wide. Camcorders based on this format are small too.

Professional Video Formats
Name Tape
size
Video Compression
ratio
Data
transfer
rate
Vendor Highlights
Betacam
SP
½” Component     Sony Used by TV
channels
Betacam
SX
½” Component MPEG-2
compression
18 Mbps Sony For news
gathering
Digital
Betacam
½” Component 2:01 Up to 90
Mbps
Sony For making
copies from a master, as copies don’t lose quality as they do in betacam
D1 ¾” Component Uncom-pressed Up to 270
Mbps
Sony High
quality, very costly
D2 ¾” Composite Uncom-pressed Up to 143
Mbps
Ampex and
others
Initially
used for ENG (electronic news gathering) High quality, very costly
D3 ½” Composite Uncom-pressed Up to 143
Mbps
Panasonic  For
professional camcorders
D5 ½” Composite Uncom-pressed Up to 170
Mbps
Panasonic D5 machines
can play D3  tapes, but not
vice versa
D6 ¾” Component Compressed     Uses D1
tape, used as recorder for HDTV
D7
or DVC PRO
¼” Component 5:01 25 Mbps Panasonic,
Philips and others
DVC PRO can
play DV and DVCAM. Much lower  in cost to work with than beta or digibeta
DVC
PRO 50
¼” Component 3.3:1 25 Mbps Panasonic Players can
play DVCAM tapes but not vice versa. Used for professional post-production
work
DVCAM ¼” Component 5:01 25 Mbps Sony Extension
of DV format. Can play DV tapes, but not DVC PRO or DVC PRO 50
D9
or Digital-S
½” Component 3.3:1 Up to 50
Mbps
JVC Digital-S
systems can also play older S-VHS tapes
M-II ½” Component     Panasonic
and JVC
Tape runs
at six times the normal speed

MicroMV. A recent format introduced by Sony in its digital camcorders, this uses MPEG-2 compression and records DV-quality signals on tapes much smaller than MiniDV cassettes. Video is recorded on these at 12 Mbps, which is an even lower, and therefore much less resource-hungry, rate than
DV. 

Digital 8. The digital counterpart of the Hi8 or 8 mm format. The tape is 8 mm wide, and compressed component video is recorded. The camcorder can play older Hi8 or 8 mm tapes as well. The compression ratio is 5:1 and data transfer rate is 25 Mbps. Recording on 8 mm videotape is done at double the normal speed–that is, a two-hour tape will take only one hours of recording on a Digital 8 camcorder.

Hi8. An 8 mm analog format popular with home users before digital formats came in. It’s still around and plays better than its predecessor, the 8 mm tape.

VHS (Video Home System). This is the (analog) format that plays on your VCR. VHS is also used in video assist in post-production work. Though VCDs are making their presence felt, VHS is still around.

S-VHS. An analog format that plays about 70 percent better than the VHS. 

DVD. Though this has been slow to catch up in the video recording and playback market, Hitachi has announced a camcorder that can record on
DVD-RAM media.

On your PC
Here we are on familiar terrain, as you’ll know most of these formats.

AVI (Audio Video Interlaced). One of the granddaddies in the video market. Introduced by Microsoft with Windows 3.1, the early video-editing systems and software used this format by default. It is still used in video-editing cards to capture video clips at low resolutions.

MOV. A format in the Mac world and the proprietary standard of Apple’s Quicktime. It supports streaming video as well, but the advent of MPEG has pushed it towards the wings.

MPEG (Motion Picture Experts Group). A popular set of standards today. MPEG-1 is for low-bandwidth applications, suitable for home or semi-professional use. It allows a data rate of 1-1.5 Mbps. MPEG-2 allows data rates of up to 100 Mbps and can be used for digital TV or video films on DVD-ROM. Formats like Betacam SX use MPEG-2 compression to achieve low data transfer rates. MPEG-2 also finds application in the home-video segment. The other two standards here are MPEG-4 and MPEG-7.

DivX and Open DivX. Based on Microsoft’s MPEG-4 compression, DivX became popular in the hacker underground for its ability to rip a movie off a DVD and compress it to one-fifth of the original size, so that a whole Hollywood movie that took up about 5 GB space on a DVD, could fit onto a single 650 MB CD-ROM, or on your hard disk. It’s raised a lot of hackles in a world of copyrights, but the format is alive and kicking.

OpenDivX is a parallel development, coming out from an open-source project called Project Mayo, and is similar to DivX because both are based on MPEG-4 compression. It’s claimed to be an improvement over
DivX.

MJPEG (Motion JPEG). This results in a series of JPEG images. It is a compression method used by video-editing cards to
reduce the data transfer rate of a TV signal to about one fifth its original size, equivalent to 5:1 compression. 

There are also VCD, SVCD, DVD and miniDVD formats, for recording and disseminating video.

TV watching
We now come to TV signal encoding and how the formats you watch movies in are related to this.

Video and TV
Unlike CRT monitors, which are non-interlacing, TV uses interlacing. An electron beam passes from the top to bottom once filling alternate lines and then filling the lines in between. Video formats for TV use this method, but are different for different regions of the world. 

There are three main standards–NTSC, PAL and SECAM. While the US and Japan use NTSC (National Television Standards Committee), PAL (Phase Alternation by Line) is popular in Asian and European countries, including India.

SECAM (Systeme Couleur Avec Memoire), very similar to PAL, is used in France, Russia and some East European countries. These standards are incompatible with each other, so that video recorded in NTSC cannot run on Indian TV sets or VCRs as it is. When you convert film (typically captured at 24 fps) to video, or digitize analog output from a TV or VCR in your PC, your calculations of video capture and frame rate conversion will depend on the standard you’re working with.

NTSC. This draws 525 lines 60 times per second, using an AC electric current at 60 Hz. This makes a picture rate of 30 fps (since 30 fields are drawn per second). NTSC has the advantage of less visible flicker because it uses more frames per second than PAL or SECAM, and a higher signal to noise ratio because of low bandwidth. The less number of scan lines, however, means that the picture is less clear on large-screen TVs.

PAL. There are two main PAL standards. PAL-M draws 525 lines 60 times per second, giving a frame rate of 30 fps, at a vertical frequency of 60 Hz. Its horizontal frequency at 15.750 kHz is more than that of NTSC at 15.734 kHz. PAL-N draws 625 lines 50 times a second, giving a frame rate of 25 fps at a vertical frequency of 50 Hz. The advantage comes from clearer picture with more scan lines, but the disadvantage is more flicker because of the lower frame rate, and more picture noise (lower signal to noise ratio) because of the higher bandwidth channel.

SECAM. SECAM is very close to PAL, running at 625 lines per frame and a frame rate of 25 fps. The difference is that color information is transmitted sequentially here. Its pros and cons are almost similar to those of PAL-N. 

The Aspect Ratio
Aspect ratio is the ratio of the width of a screen to its height. This affects video broadcasting as a film made for the theaters is made using a certain aspect ratio, but when it’s shown on TV, the aspect ratio has to be changed so that the movie can fill the TV screen. This has sparked a debate because a lot of movie buffs don’t like the original work being tampered with. Current DVDs, however, give you the option of watching a film in its original widescreen format. Here are some of the aspect ratios in use.

4:3. Also expressed as 1.33:1, this is the aspect ratio of your TV, where the width is 1.33 times the height of the TV screen. The actual aspect ratio of 35 mm film is also 1.33:1, and many silent Hollywood movies were shot in this ratio. Incidentally, the aspect ratio of TV was defined as 1.33:1, because it was the ratio of 35 mm film. 

Academy ratio. This is a ratio of 1.37:1, and was used for most Hollywood films until the 1950s. During the 1950s, when TV took off and movie studios needed to woo audiences, shooting films in wider aspect ratios became a way of doing so. It gave filmmakers more room for panoramic shots and artistic compositions. 

Two of these ratios are particularly popular today. One is Academy Flat, popularly known as Flat. This is a ratio of 1.85:1. The English Patient was one of the films shot in this ratio. The other is Anamorphic Scope. An aspect ratio of 2.35:1–the width is a whopping 2.35 times the height–makes this widescreen format just the thing for spectacular films like Star Wars. The ratio is popularly called Scope.

There are lesser-used widescreen ratios as well, like 1.66:1 or 2.20:1 (for 70 mm film).

Letterbox or widescreen. Here, when a movie is transferred to DVD for home viewing, it is transferred in exactly the same aspect ratio, and is displayed in the center of the TV screen with black bars above and below. So, although your viewing area is less than the size of your TV screen, you see everything the way the director intended you to see it.

Full-frame. This recording uses the full TV screen, and is usually created using ‘pan and scan’. Here, the operator or video camera scans the entire widescreen movie and decides which part of the action in each shot to keep for your TV screen, and which to discard. So, what you see is a modified version of the original. 

16:9. Most recent widescreen digital and analog TVs are based on this ratio of 1.78:1. This is very close to the 1.85:1 ratio used in many Hollywood movies, so that whether you watch it in full-frame or letterbox, you wouldn’t lose too much from the original version. The problem, however, is that even if you have a widescreen or letterbox movie, it won’t occupy the full screen of a widescreen TV because the DVD was created for a 1.33:1 aspect ratio.

This is one of the reasons for the advent of anamorphic DVDs, which make the most of conventional TVs and widescreen ones. If you have one of these and a conventional TV (1.33:1), you’ll see the film in letterbox format; but if you have a widescreen TV (1.78:1), you’ll have a movie that fills the screen and doesn’t lose out much from the original. Given that future digital TV will be widescreen, these DVDs will keep you entertained for a long, long time.

Pragya Madan

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