This page discusses some frequently asked questions
about HDS Video operations.
Frequently Asked Questions:
These are questions often asked about HDS ViewStation video
operations.
HOW DOES VIDEO AFFECT MY NETWORK?
The HDS netTV Simulcast client does several things:
1.
Receives video (and audio) from its analog source
2. Converts the
analog data (video and audio) to digital format
3. Compresses the
video data using Sun's CELL-B compression algorithm
4. Transmits the compressed data over the Ethernet using IP
Multicasting
The HDS netTV Simulcast client has two slider bars that let
you adjust the impact of the multicasting load on the network. These
two slider bars are "Quality" and "Net Use Limit" on the Network
Controls menu. They control the amount of compression used by the
Simulcast client.
The HDS netTV viewer client reports the frame rate it is
receiving and the traffic generated on the network. These are affected
both by the compression setting and also by the content of the video
image (CELL-B compression doesn't send the entire video image with each
frame, but only the pixels changed since the last frame. Therefore, an
image of rapid movement has much more data to be compressed than an
image of a "talking head" against a static background).
The examples shown below illustrate several possibilities. In
these cases, the "Quality" slider was set to 0%, 50%, and 100% with the
results as recorded. The "Net Use Limit" was not restricted in these
tests. Compression was turned On.
Case 1: Maximum
Compression (maximum frame rate)
Capture size: 160x120 pixels
Quality: 0
Frame Rate: 34 frames per second
Bits
per second: 200,000 average
% of Ethernet: 200,000/5,000,000 =
4%
% of switched Ethernet: 200,000/10,000,000 = 2%
Case 2: Average Compression
Capture size:
160x120 pixels
Quality: 50
Frame Rate: 30 frames per
second
Bits per second: 400,000 average
% of Ethernet:
400,000/5,000,000 = 8%
% of switched Ethernet:
400,000/10,000,000 = 4%
Case 3: Maximum Quality (minimum compression)
Capture
size: 160x120 pixels
Quality: 100
Frame Rate: 22 frames
per second
Bits per second: 730,000 average
% of
Ethernet: 730,000/5,000,000 = 15%
% of switched Ethernet:
730,000/10,000,000 = 7%
HOW LARGE ARE DIGITAL VIDEO FILES IN DIFFERENT FORMATS?
There are two principal variables to consider: first, the
resolution size of the image (either 160x120 or 320x240 pixels);
second, the audio component of the files.
We've examined some .avi files which use Indeo 3.1
compression. The audio tracks in the files were recorded in mono at 11
KB/sec. The 160x120 image files occupy approximately 3 MB of file space
per minute of video (the audio portion of the file represents about 22%
of the file size). The 320x240 image files occupy approximately 9 MB of
file space per minute of video (the audio portion of the file
represents about 7% of the file size).
WHAT DO I NEED FOR MY IN-HOUSE VIDEO TRAINING?
A typical training application in a university setting uses HDS
ViewStations with video features. A laboratory classroom uses a
ViewStation with netVideo and a video camera and microphone. This
ViewStation captures the professor with his lectures and exhibits, then
uses the netTV Simulcast client to send this video and audio to other
ViewStations on the network, in this case in several different class
rooms across the campus.
The equipment needed for this simple installation is one
ViewStation with HDS netVideo (along with appropriate cameras,
microphones, etc.), and as many other ViewStation FX models with HDS
netTV Viewer software and audio capability as needed.
Other training techniques include preparation of instructional
video tapes which are broadcast at scheduled times on an HDS netVideo
unit to other ViewStations on the network. This is an easy way to
create an internal broadcast network for your company.
WHAT ARE SOME OTHER APPLICATIONS FOR NETVIDEO
VIEWSTATIONS?
Two of HDS's customers use their ViewStations for emergency
response services, in one case for a municipal emergency response
center, and in another case for a disaster control center for a
regional communications company.
In the emergency response center, the netVideo ViewStation
receives TV signals from a remote camera at the emergency site via a
private cable channel broadcast. This is then multicast to other
ViewStations (along with news and weather channel information). Since
the ViewStations are full-featured X terminals, the operators have
access to multiple host computers for database information and dispatch
to support their on-site teams.
The disaster control center is a centralized regional group
that relies on netVideo ViewStations to monitor problems via TV news
and weather channels, with internal distribution at the center via the
ViewStation's multicasting client. They also use extensive
teleconferencing to local offices with the ViewStation, which is
especially efficient because of their high-speed networks and routing.
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