Dahua Bandwidth Consumption / Strange VBR Performance

Here is the scenario:

Dahua IPC-HDBW5302 3MP Dome

Main Stream Profile Example 1:

  • 3MP Resolution
  • 10FPS
  • Quality 6
  • VBR
  • Cap 4Mbps

Main Stream Profile Example 2:

  • 3MP Resolution
  • 10FPS
  • Quality 3
  • VBR
  • Cap 4Mbps

Now this camera is being recorded by Digital Watchdog Spectrum (HD Witness) and both of these examples result in the same output to the VMS. The information feature in DWS shows 10.00FPS and a bitrate fluctuating between 3.5 and 4.3 with a pretty static scene.

The question that I have is this; Is the quality (compression) setting in reality a cap?

I say this because changing between 3, 4, 5, or 6 quality doesn't affect bitrate or framerate (framerate stays constant at 10.00FPS no matter what we change) to the VMS. Only changing the quality setting below 3 seems to keep the bitrate below the cap of 4Mbps. Since we haven't seen any framerate loss, stays at 10.00FPS constant, we have to be losing quality (higher compression) in order to stay under the VBR cap.

Now, when we raise the VBR cap to 8Mbps (highest allowed for this unit), we see the bitrate bump up about 1Mbps to 4.5 to 5.3Mbps with the quality setting set to 3. This seems to be the bitrate for this given scene for quality 3.

Now when we increase the quality level above 3, the bitrate hits the full 8Mbps cap.

So, it appears that the quality (compression) setting is also a cap. We don't think we are even able to encode above quality 4 on this unit in this given scene. Is this common with other brands as well? Is this a Dahua only issue?

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