Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
Burn-In – Component testing method used to screen out early failures by
running the circuit for a specified length of time.
Burst – A small reference packet of the subcarrier sine wave, typically 8
or 9 cycles, which is sent on every line of video. Since the carrier is suppressed,
this phase and frequency reference is required for synchronous
demodulation of the color information in the receiver. Refer to the
Horizontal Timing discussion.
Burst Gate – This signal tells the receiver valid color ready for use.
Bus – a) Any row of video crosspoints that allow selection of various
sources to be selected, and the associated row of buttons for such selection.
Buses are usually associated with a given M/E or the DSK although
they may be independent as in aux buses. Also, any row of video or key
source selections which may or may not be selected by push buttons on a
bus row. For example, key video selections on Ampex switchers appear on
buses which are accessed and selected by keypads. Due to the fact that
there is no associated row of buttons, this arrangement is called a “phantom
bus.” b) A parallel data path in a computer.
Bus Address – A code number sent out to activate a particular device on
a shared serial or parallel bus interface. Also, the identification number of a
device.
Bus Conflict – Conflict that occurs when two or more device outputs of
opposite logic states are placed on a three-state bus at the same time.
Bus Controller – Generates bus commands and control signals.
Bus Driver – An IC that is added to a bus to provide sufficient drive
between the CPU and the other devices that are tied to the bus. These are
necessary because of capacitive loading, which slows down the data rate
and prevents proper time sequencing of microprocessor operation and/or
to overcome resistive loading when fan-out requirements increase.
Bus Keyer – A keyer that does a key on top of the bus video before the
signal gets to the M/E. On the 4100, these are packaged as “dual bus keyers”
and are the modules between the bus rows and the M/Es. On the AVC,
bus keyers are integral with the M/E module, with controls in a similar
location.
Bus Row – Any row of video source select buttons allowing immediate
selection of switcher video sources.
Bus Termination – Method of preventing reflections at the end of a bus.
Necessary only in high-speed systems.
Buss – In video switching equipment, a wire carrying line-level signals
(anything greater than mike level).
Button – On a mouse, a button is a switch that you press with a finger. In
a window on your screen, a button is a labeled rectangle that you click
using the cursor and mouse.
BW – See Bandwidth.
24 www.tektronix.com/video_audio
BWF (Broadcast WAV Format) – Broadcast WAV Format is an audio file
format based on Microsoft’s WAV Format that carries PCM or MPEG encoded
audio. BWF adds the metadata, such as a description, originator, date
,and coding history, needed for interchange between broadcasters.
B-Y – One of the color difference signals used in the NTSC system,
obtained by subtracting luminance from the blue camera signal. This is the
signal that drives the horizontal axis of a vectorscope. The human visual
system has much less acuity for spatial variation of color than for brightness.
Rather than conveying RGB, it is advantageous to convey luma in one
channel, and color information that has had luma removed in the two other
channels. In an analog system, the two color channels can have less bandwidth,
typically one-third that of luma. In a digital system each of the two
color channels can have considerably less data rate (or data capacity) than
luma. Green dominates the luma channel: about 59% of the luma signal
comprises green information. Therefore, it is sensible, and advantageous
for signal-to-noise reasons, to base the two color channels on blue and
red. The simplest way to remove luma from each of these is to subtract it
to form the difference between a primary color and luma. Hence, the basic
video color-difference pair is (B-Y), (R-Y) [pronounced “B minus Y, R minus
Y”]. The (B-Y) signal reaches its extreme values at blue (R = 0, G = 0,
B = 1; Y = 0.114; B-Y = +0.886) and at yellow (R = 1, G = 1, B = 0;
Y = 0.886; B-Y = –0.886). Similarly, the extreme of (R-Y), + –0.701,
occur at red and cyan. These are inconvenient values for both digital and
analog systems. The color spaces YPbPr, YCbCr, Photo YCC, and YUV are
simply scaled versions of (Y, B-Y, R-Y) that place the extreme of the color
difference channels at more convenient values.
Byte – a) A complete set of quantized levels containing all of the bits.
Bytes consisting of 8 to 10 bits per sample are typical. b) Group of eight
bits. Can be used to represent a character. Microcomputer instructions
require one, two, or three bytes. A word can be one or more bytes. c) A
group of adjacent binary digits operated upon as a unit, capable of holding
one character in the local character set, and usually shorter than a computer
word (frequently connotes a group of eight bits). Current usage within
the context of electronic production concerns is tending to define a byte as
eight bits to have a consistent data unit for measuring memory capacities,
etc. d) 8 bits. The combination of 8 bits into 1 byte allows each byte to
represent 256 possible values. See Megabyte, Gigabyte, Terabyte.
1 byte = 8 bits = 256 discrete values (brightness, color, etc.)
1 kilobyte = 1,024 bytes (not 1000 bytes)
1 megabyte = 1,048,576 bytes (not one million bytes)
1 gigabyte = 1, 073,741,824 bytes (not one billion bytes)
1 terabyte = 1,099,511,627,776 bytes (not one trillion bytes)
Byte Aligned – A bit in a coded bit stream is byte-aligned if its position is
a multiple of 8-bits from the first bit in the stream.