User Manual

Tech-X Flex
®
(P5) Verizon Base Unit User Guide Rev B PRELIMINARY 3/20/2014
5-31
Intro
Wi-Fi
10/100
System
IP/Video
Specs
Digital video concepts overview
About basic video and audio compression
Compression techniques are vital to allow modern communication networks to handle the transmission
of packetized digital video. For example, without compression, a video stream with pixelized image
frames would require a large amount of data, far too much for efficient transport across networks to
multiple subscribers.
Video compression involves multiple stages, beginning with the removal of spatial similarities from
individual frames using techniques similar to JPEG (Joint Photographic Experts Group) compression.
Then, similarities between adjacent frames are determined and removed from the stream, using complex
algorithms to reuse identical data that was already transmitted and to “predict” data where future
changes can be estimated. These processes serve to reduce the two primary forms of redundancy:
• Spatial redundancy - Within any given video frame, certain data may be redundant, such as large
portions of the same color or geometrical design. In this situation, compression may be employed to
represent portions of the frame as smaller mathematical values, rather than expressing every single
pixel individually, when many pixels are the same.
• Temporal redundancy - Adjacent video frames often have many similarities, especially with video of
still or slow-moving objects. In this case, sequential frames may have redundant information
expressed over time as the video is played.
In the end, the encoders/decoders effectively form a system where the technology is able to interpolate
redundant data, without the need to transmit it. This system allows for more efficient network capacity
utilization when transporting audio/video streams over communications networks.
Frame types
As part of the reduction in redundancy, the video is compressed and reorganized into three different
frame types, serving individual roles as follows:
EMM Entitlement Management Messages represent private conditional
access information that specifies the authorization levels or the
services of specific decoders. They may be addressed to single
decoders or groups of decoders. When the CA descriptor is found in
the CAT section (table_id=0x01) the CA_PID points to packets
containing system-wide and/or access control management
information such as EMMs.
Name/abbrev. Stream type