Axis Communications Video Server 243Q Blade - Manual (Page 20)

20 AXIS 243Q Blade - Video & Image
Adjusting the Maximum bit rate and setting it to Variable or Constant helps control the
bandwidth used by the MPEG-4 video stream.
Bit Rate control
Adjusting the maximum bit rate and setting it to variable or constant is a good way of
controlling the bandwidth used by the MPEG-4 video stream.
Leaving the Maximum bit rate as unlimited will provide consistently good image quality,
but at the expense of increased bandwidth usage whenever there is more activity in the
image.
Limiting the bit rate to a defined value will prevent excessive bandwidth usage, but images
will be lost when the limit is exceeded.
Note that a maximum bit rate can be used for both variable and constant bit rates.
The bit rate type can be set as Variable Bit Rate (VBR) or Constant Bit Rate (CBR). VBR
will adjust the bit rate according to the images' complexity, and thus uses a lot of
bandwidth for a lot of activity in the image and less when the monitored area is quiet.
When using CBR you can set a fixed Target bit rate, which will ensure that the level of
bandwidth consumed is predictable and will not change, whatever happens in the image.
Priority - As the bit rate would usually need to increase for increased image activity, but
cannot when CBR is selected, the frame rate and image quality will both be affected
negatively. To go some of the way towards compensating for this, it is possible to prioritize
either the frame rate or the image quality whenever the bit rate would normally need to be
increased. Not setting a priority means the frame rate and image quality will be affected
approximately equally.
Video Stream
This parameter can be set to frame rate to increase the frame rate by 30% in 4CIF
resolution. This means that under normal conditions the maximum frame rate can be
increased from 17 fps to 22 fps in PAL, and from 21 fps to 27 fps in NTSC.
Note also that depending on the amount of motion, this may also increase the required
bandwidth by 1-15% for each frame.
This parameter has no effect when the resolution is set to lower than 4CIF, although there
is a risk of increased bandwidth usage. In this case the parameter should be set to
bandwidth.
For more information on MPEG-4 settings, refer to the online help .