NCast Presentation Recorder Reference Manual
4.6.2. 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.
At HD720 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.
4.6.3. Bit Rate
The video bit-rate in kilobits-per-second defines the maximum bit-rate that the encoders may utilize in
creating the media stream. For static images the bit-rate may decrease from this peak level.
The following table lists the absolute minimum recommended bit-rates for high frame-rates:
Resolution
Minimum Bit-rate
Preferred Bit-rate
QVGA (320x240)
128 kbps
192 kbps
VGA (640x480)
220 kbps
330 kbps
SVGA (800x600)
310 kbps
465 kbps
HD720 (1280x720)
550 kbps
1500 kbps
HD1080 (1920x1080)
1000 kbps
2000 kbps
Settings below these values will generate pixelation and other visual artifacts in the received image. Also,
use of the minimum bit-rates will increase end-to-end latency, may reduce the visual clarity of the image
and introduce lip-synch problems. As with any other type of compression system, there is a complex
interaction between bit-rate, frame-rate, image resolution, and end-to-end latency. For HD720 images,
settings above 1000 kbps generally produce excellent results. The lowest latency is achieved by setting
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