Axis Communications 243Q Blade user manual Bit Rate control

AXIS 243Q Blade - Video & Image 20

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 .