Member Discussion

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?

If you want to know what the actual 'quality' level is, use Avinaptic to measure its H.264 quantization level. To do so, connect the Dahua camera to VLC, record clip, open clip with Avinaptic and check quantization level. Repeat for different Dahua quality levels and compare. See: How to Measure Video Quality / Compression Levels.

The method above will tell you definitively if the actual compression levels are being adjusted.

As for your description, it appears that your 4Mb/s cap is too low relative to the settings and scene you have. I suspect this because you say bandwidth is constant, even when changing quality levels at 4Mb/s cap, but bandwidth varies when increasing the cap.

The one really weird thing here is that bandwidth consumption is so high. What is the scene here? How busy / active / complex is it? White wall? Intersection?

It is an indoor gun range, which is just a bunch of concrete floor and walls in the camera view. There was no motion or movement in the cameras view. The light levels were somewhat low, probably under 10 lux, but we didn't measure. I will try turning on all the lights today to see how much lighting affects the bandwidth.