NCast Telepresenter M4 - Manual (Page 47)

NCast Telepresenter Reference Manual
For the lowest bit rate, 128 kbps, a resolution of 640x480 and a frame-rate of 5 frames/second for graphics
or 10 frames/second for video are recommended.
There is no way to define the optimum settings for a given application. It depends on the material being
presented, the expectations for motion smoothness and embedded video performance, the equipment
available to the receiving audience, the maximum network bandwidth available, and other factors. The only
way to determine the optimum settings for a particular installation is to run tests on the material being
presented using the network at hand.
4.2.7. Video Frame-rate
The video frame-rate represents the number of frame (visual image) grabs per second the system will
attempt to achieve. The range of this setting is 1-60 frames per second. For NTSC video encoding a full 30
frames/second is achieved.
At XGA resolutions, dropping the frame rate to lower values (5 frames/second, for example) allows a broader
range of lower performance PCs to successfully decode the received presentations. It also reduces the
required network bandwidth. At these rates, however, cursor movements look somewhat jerky and
embedded video clips do not play well. One tradeoff might be to send a lower resolution (SVGA, 800x600)
image at a higher frame-rate.
At settings of 10 frames/second cursor movement and drop-down menus look natural, but video still suffers.
At 15 frames/second video playback starts to become acceptable, but high-motion imagery has detectable
artifacts. At the higher rates of 20 frames/second and up both the video and graphics performance look
natural. These high frame-rates deliver smooth animation and video playback that most viewers will find
acceptable.
4.2.8. Video MTU
The Maximum Transmission Unit (MTU) is the maximum length of a packet and is normally set to 1500. For
some special circuits (satellite links, others) the maximum size may need to be adjusted downward to avoid
packet fragmentation, which leads to inefficiencies and possible packet loss.
When using N-Way bridging, this value should be set to 1476.
4.2.9. Audio Address
An address entered for Audio (the Audio media stream) will be either a valid multicast address, or the
numeric host IP address of the remote unit if a point-to-point connection is being established.
For a discussion of multicast addresses, see the discussion above (Graphics addresses).
All units in one session use the same multicast address. The Graphics, Audio and Collaboration multicast
addresses for a session can be the same if the Port numbers are different. Units engaged in different
sessions should use different multicast addresses to minimize traffic loading on the network (the multicast
routers distribute all traffic to all points subscribed on a particular multicast address, independent of the port
number).
If the network is not multicast enabled, point-to-point communications between two Telepresenters is
possible by entering the numeric IP address of the remote unit into this field.
To disable multicasting of a session (e.g. in a record-only situation), set all multicast addresses to
“127.0.0.1”.
4.2.10. Audio Port
The port number assigned to the audio media stream.
See the discussion above (Graphics ports) for more detailed information on ports.
4.2.11. Audio Format
This menu pulldown selects the bandwidth and encoding properties of the audio media stream associated
with the graphics stream. All audio is encoded in the Advanced Audio Coding (AAC) format. Different bit-
rates and an optional stereo setting provide for a wide selection of audio formats to be associated with the
graphics media stream.
NCast Corporation Revision 2.2
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