Axis Communications 211M user manual Advanced MPEG-4 Settings, GOV Settings, Bit Rate Control

AXIS 211M - Video and Image settings

Advanced - MPEG-4 Settings

GOV Settings

The GOV structure describes the composition of the MPEG-4 video stream. Setting the GOV-length to a high value saves considerably on bandwidth. The Cyclic refresh parameter gives a smoother bit rate and can be useful if bandwidth is limited.

Note: Cyclic refresh should not be enabled if Event handling is enabled and the file format is set to MPEG-4 in Upload images/video (see Setup > Event configuration > Event settings).

Bit Rate Control

Limiting the maximum bit rate 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, thus using a lot of bandwidth for a lot of activity in the image and less for lower activity in the monitored area.

CBR allows you to set a fixed Target bit rate that will consume a predictable amount of bandwidth, and which will not change whatever happens in the image.

As the bit rate would usually need to increase for increased image activity, but in this case cannot, the frame rate and image quality will 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.

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