Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
A–Advanced.
A and B Rolls, Tape – Separation of material into two groups of reels (A
rolls and B rolls), with alternate scenes on each reel pair (A reel and B reel)
to allow transitions between reels.
A Bus – The top row of the two rows of video source select buttons associated
with a given M/E.
A Bus Keyer – A keyer that appears only on top of an “A” bus background
video on an M/E.
A/A (A/X/A) Roll Editing – Editing from a single source using effects to
transition from the source to itself (source “A” to “A”) using a picture freeze
at the end of one scene to transition the start of the next scene.
A/B Roll – Creating fades, wipes and other transitions from one video
source to another.
A/B Roll Editing – Editing from two source VCRs (“A” and “B”) to a third
(recording) VCR. Typically a switcher or mixer, such as the Digital Video
Mixer, is used to provide transition effects between sources. Control over
the machines and process can be done manually or automatically using an
edit controller.
A/D – See A-to-D Converter.
A/V – Audio/Video.
A/V Edit – An edit that records new audio and video tracks. Also called
Straight Cut.
A/V Mixer – See Audio/Video Mixer.
A:B:C Notation – The a:b:c notation for sampling ratios, as found in the
ITU-R BT.601 specifications, has the following meaning: a) 4:2:2 means
2:1 horizontal downsampling, no vertical downsampling. Think four Y samples
for every two Cb and 2 Cr samples in a scan line. b) 4:1:1 ought to
mean 4:1 horizontal downsampling, no vertical. Think four Y samples for
every one Cb and one Cr samples in a scan line. It is often misused to
mean the same as 4:2:0. c) 4:2:0 means 2:1 horizontal and 2:1 vertical
downsampling. Think four Y samples for every Cb and Cr samples in a scan
line. Not only is this notation not internally consistent, but it is incapable of
being extended to represent any unusual sampling ratios, that is different
ratios for the Cb and Cr channels.
AAL – ATM Adaptive Layer.
AAL5 – ATM Adaptation Layer 5.
AAU (Audio Access Unit) – See Access Unit.
A-B Rolls – Duplicate rolls of videotape information having identical time
code; required to achieve effects of dissolves.
ABC – Television network financially supporting development of ACTV and
pioneering the use of digital video transmission.
ABKW – See Audio Breakaway.
Abort – Halts the program and returns control to the operator or operating
system.
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Absolute Time Code – Absolute time code (ATC) is generally recorded in
the subcode or control track region of any digital tape. This is the code that
digital tape machines use to locate specific points on a tape for autolocation
or other functions. In some machines, it is even used to synchronize
the tape to other equipment. ATC is precisely accurate and usually conforms
to the IEC standard which is easily converted to the more commercially
used SMPTE time code. Unlike SMPTE, ATC always begins at zero at
the beginning of a digital tape and increments one frame at a time until
recording stops. Some DAT machines have the ability to function without
ATC on a tape while others simply will not play a tape without it. These
days, almost all machines record it automatically so it will always be on
every tape.
Absorption – In acoustics, the opposite of reflection. Sound waves are
“absorbed” or soaked up by soft materials they encounter. Studio designers
put this fact to work to control the problem of reflections coming back to
the engineer’s ear and interfering with the primary audio coming from the
monitors. The absorptive capabilities of various materials are rated with an
“Absorption Coefficient.”
Absorption Coefficient – a) A measurement of the absorptive characteristics
of a material in comparison to air. b) A measure of the relative
amount of sound energy absorbed by the material when a sound strikes its
surface.
ABU – Asia-Pacific Broadcasting Union.
AC Bias – The alternating current, usually of frequency several times higher
than the highest signal frequency, that is fed to a record head in addition
to the signal current. AC bias serves to linearize the recoding process
and is universally used in analog recording. Generally, a large AC bias is
necessary to achieve maximum long-wavelength output and linearity, but a
lower value of bias is required to obtain maximum short-wavelength output.
The mechanism of AC bias can best be explained in terms of anhysteresis.
AC Coefficient – Any DCT coefficient for which the frequency in one or
both dimensions is non-zero.
AC Coupled – a) AC coupling is a method of inputting a video signal to a
circuit to remove any DC offset, or the overall voltage level that the video
signal “rides” on. One way to find the signal is to remove the DC offset by
AC coupling, and then do DC restoration to add a known DC offset (one
that we selected). Another reason AC coupling is important is that it can
remove harmful DC offsets. b) A connection that removes the constant
voltage (DC component) on which the signal (AC component) is riding.
Implemented by passing the signal through a capacitor.
AC Erasure – See Erasure.
AC-3 – Audio Coding algorithm number 3. An audio-coding technique used
with ATSC. The audio compression scheme invented by Dolby Laboratories
and specified for the ATSC Digital Television Standard. In the world of consumer
equipment, it is called Dolby Digital.
ACATS (Advisory Committee on Advanced Television Service) – A
group comprised almost exclusively of presidents, chief executive officers,