Glossary
Electra VS
- Version 05.10 599
User Manual
- Rev. A
PCR
Program Clock Reference.
A time stamp used in digital video compression that indicates the system
time clock’s (STC) value the instant the time stamped packet leaves the
encoder. In the Moving Pictures Experts Group 2 (MPEG-2) system the
digital video source is clocked at 27 MHz and the decoder must generate
the same 27 MHz clock so that the encoder and decoder clocks are
synchronized. These clocks are called System Time Clocks (STC). To
synchronize the decoder, the encoder sends a PCR to the decoder. The
decoder receives the packet and compares the STC value with its own STC
counter value. If the values are the same then no adjustment is needed but
if the two values are different, the decoder must either reset, speed up, or
slow down its STC.
PES
Packetized Elementary Stream
A specification in the MPEG-2 Part 1 (Systems) (ISO/IEC 13818-1) and ITU-T
H.222.0[1][2] that defines carrying of elementary streams in packets within
MPEG program streams and MPEG transport streams [3]. The elementary
stream is packetized by encapsulating sequential data bytes from the
elementary stream inside PES packet headers.
PID
Packet Identifier
A unique integer value used to identify the contents of an MPEG-2
Transport Stream packet (Video component PID, Audio component PID,
etc.).
Profile
A defined subset of the syntax specified in the MPEG-2 or MPEG-4 video
coding specification.
PMT
Program Map Table.
A mandatory MPEG-2 PSI table. Each service has a PMT. It lists the service
component parts (elementary streams of video, audio, location of the PCR
fields, etc.).
POIS
Placement Opportunity Information System.
POIS is defined in the Real-time Event Signaling and Management API
specification (ESAM) from CableLabs®.
PSU
Power Supply Unit.
QCIF
Quarter Common International Format.
To have one fourth of the area as "quarter" implies the height and width of
the frame are halved (video size: 176p x 144p).
QSIF
Quarter Screen International Format.
To have one fourth of the area as "quarter" implies the height and width of
the frame are halved (video size:160 x 120 pixels (NTSC) or 192 X 144 pixels
(PAL).
QVGA
Quarter Video Graphics Array.
QVGA is a popular term for a computer display with 320×240 display
resolution.
R, G, B
Red, Green, Blue.
Resolution
Determined by the number of pixels displayed per line or for a given area.
RTP
Real Time Transport Protocol.
T
his Protocol defin
es a s
tandardized packet format for delivering audio
and video over IP networks.
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