Video Glossary of Terms

 

16:9

The aspect ratio most commonly known is widescreen or letterbox. 16:9 is the standard aspect ratio used in the production of video for display in theatres and on HDTV (High Definition Television).

 

4:3

Traditional nearly square aspect ratio used for most current analogue television sets. This aspect ratio will slowly be phased out in favour of the wider, more panoramic and movie-like 16:9 ratio.

 

Aspect Ratio

Aspect ratio is the width-to-height ratio of an image. A 4:3 aspect ratio means the horizontal size is a third again wider than the vertical size. Standard television ratio is 4:3 (or 1.33:1). Widescreen DVD and HDTV aspect ratio is 16:9 (or 1.78:1).

 

AVI

Audio Video Interleaved - A multimedia file format for storing sound and video. Since an AVI file can use different codecs and formats there is no standard format for an AVI file.

 

Bit Rate

Bit rate is the average number of bits that one second of video or audio data will consume. Higher bit rate means bigger file size and generally higher quality video or audio quality while lower bit rate has a lower file size quality of video or audio is reduced.

 

Capture

Capture means to capture video or TV/Satellite signals to disk. This can include firewire capture from DV cameras.

 

Codec

An acronym for compression/decompression, a codec is a specialized computer program that compresses or reduces the number of bytes consumed by large files and programs. Files encoded with a specific codec require the same codec for decompression. An example of a codec is DivX.

 

Component video

A video system containing three separate colour component signals, either red/green/blue (RGB) or chroma/colour difference (YCbCr, YPbPr, YUV), in analogue or digital form. The MPEG-2 encoding system used by DVD is based on colour-difference component digital video. Very few televisions have component video inputs.

 

Composite video

Composite video is an analogue video signal in which the luma and chroma components are combined (by frequency multiplexing), along with sync and burst. It is also called CVBS. Most televisions and VCRs have composite video connectors, which are usually coloured yellow.

 

Compression

Compression is the process of removing redundancies in digital data to reduce the amount that must be stored or transmitted. Lossless compression removes only enough redundancy so that the original data can be recreated exactly as it was. Lossy compression sacrifices additional data to achieve greater compression.

 

DCT

Discrete Cosine Transform - is used to remove the spatial correlation existing among adjacent pixels in order to allow a more efficient entropy coding. The DCT coefficients have a relationship with spatial frequencies and, given that the different components have different subjective importance, DCT gives an important tool to remove also the subjective redundancy.

 

Drop Frame

Colour video was slowly introduced into broadcast. It was therefore necessary to make it compatible with black and white receivers and to design colour receivers or televisions to be able to receive black and white programming as well. In order to accommodate the extra information needed for colour, the b&w’s 30 frame/second rate was slowed to 29.97 f/s for colour. Although usually not an issue for non-broadcast applications, in broadcast the small difference between real time and the time registered on the video can be problematic. Over a period of 1 hour (SMPTE) the video will be 3.6 seconds or 108 extra frames longer in relation to the real time. To overcome this discrepancy drop frame is used.

Drop frame: Every frame :00 & :01 are dropped for each minute change (60 X 2 = 120) except for minutes with 0’s (00:, 10:, 20:, 30:, 40: & 50:) (6 X 2 = 12, 120 - 12 = 108).

 

DV

Digital Video - video captured to a PC from a digital camcorder, often through firewire. DV video data is stored usually in AVI files. Although an AVI file can have a number of streams, the most common case is one video stream and one audio stream. A raw DV stream, on the other hand, interleaves the video and audio data into a single stream.

 

DV Timecode

Also known as DV Time, a DV or MiniDV camcorder starts recording at 00:00:00. The timecode is drop frame for NTSC (minute differences in timing are made to get the film from 30 fps to 29.97 fps). DV Time is carried on the FireWire cable with the video, audio and Device Control. The biggest problem that arises with DV Time is that it resets to zero if the camera operator does not 'hook' to the end of the previously shot footage (there is an unrecorded gap between recordings).

If dealing with a miniDV or DVCAM tape with 'broken' timecode (that is in many parts), either do a clone copy to another DV tape so that the timecode is created continuously for the entire tape, or name each timecode section as a different tape.

 

DVD

Digital Versatile Disk – a high capacity optical disk that can store 4.7Gb of data. A number of different formats for DVD exist with some formats able to store more than the standard 4.7GB.

 

Firewire / IEEE1394

FireWire is a fast interconnection standard capable of transfer speeds up to 400Mbs. It works well for multimedia devices such as DV cameras and other high-speed peripherals like hard disk drives, CD/DVD burners and printers.

 

Frames per Second (fps)

Frames per second is a measure of the rate at which pictures are shown for a motion video image. In NTSC and PAL video, each frame is made up of two interlaced fields.

 

Frame

A frame is a set of scan lines in video to make a complete picture. If the video is interlaced the frame consists of both interlaced fields (half frames). If the video is progressive the frame is made up of one continuous scan from top to bottom.

 

Hi8

Hi8 is an analogue camcorder format which allows you to record video with 400 lines of resolution onto Hi8 tape, or 240 lines of resolution onto standard 8mm tape. Hi8 tapes can get up to 2hours in SP and 4hours in LP modes. Most Hi8 tapes will work in Digital8 camcorders but typically only can record 1 hour of Digital video.

 

Lossless Compression

Compression techniques that allow the original data to be recreated without loss.

 

Lossy Compression

Is a compression technique that achieve very high compression ratios by permanently removing data while keeping as much information as possible that is significant to the video. Lossy compression includes perceptual coding techniques that attempt to limit the data loss to that which is least likely to be noticed by human perception.

 

Mini DV

Mini DV is a video cassette designed for use in MiniDV digital camcorders. The picture quality of digital video recorded on a Mini DV cassette is basically identical or better to the quality of DV recorded on a Hi8 or 8mm cassette by a Digital8 camcorder. Mini DV tapes are smaller which allows for smaller camcorders.

 

NTSC

National Television Standards Committee - the NTSC is responsible for setting television and video standards in the United States (in other parts of the world, the dominant television standards are PAL and SECAM). The NTSC standard for television defines a composite video signal with a refresh rate of 60 fields (half-frames interlaced) per second. Each frame contains 525 lines and can contain 16 million different colours. The resolution of an NTSC VCD is 352x240 pixels, an NTSC SVCD is 480 x 480, and an NTSC full D1 DVD is 704 or 720 x 480.

 

PAL

Phase Alternating Line - the dominant television standard in Australia and other parts of the world. PAL delivers 625 lines at 50 fields (half-frames interlaced) per second. The resolution of a PAL VCD is 352x288 pixels, a PAL SVCD is 480 x 576, and a PAL full D1 DVD is 704 or 720 x 576.

 

Pixel

A pixel is the smallest picture element of an image (one sample of each colour component). A single dot of the array of dots that makes up a picture. The resolution of a digital display is typically specified in terms of pixels (width by height) and colour depth (the number of bits required to represent each pixel).

 

Resolution

Is the relative detail of any signal, such as an audio or video signal.

 

Sample Rate

The number of times a digital sample is taken, measured in samples per second, or Hertz. The more often samples are taken, the better a digital signal can represent the original analogue signal. Sampling theory states that the sampling frequency must be more than twice the signal frequency in order to reproduce the signal without aliasing. DVD PCM audio allows sampling rates of 48 and 96 kHz.

 

SECAM

Sequential Colour with Memory - A composite colour standard similar to PAL (image format 4:3, 625 lines, 50 Hz and 6 MHz video bandwidth), but currently used only as a transmission standard.

 

Time Code

Information recorded with audio or video to indicate a position in time. Usually consists of values for hours, minutes, seconds, and frames. Also called SMPTE time code. Some DVD-Video material includes information to allow the player to search to a specific time code position.

 

Track

Track is a distinct element of audiovisual information, such as the picture, a sound track for a specific language, or the like. DVD-Video allows one track of video (with multiple angles), up to 8 tracks of audio, and up to 32 tracks of sub picture.

 

VHS

VHS an analogue format capable of delivering 240 lines of video resolution, along with stereo sound that's nearly as good as CD (in dynamic range and frequency response).