You must be an aberration. Everyone else that I've spoken to or emailed has a problem with IVS recorded events. There is a fundamental problem with how dahua records these events. The code they use has a serious bug.
This one can handle higher wattages, but it's way more expensive.
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I don't know how to change the ISO on the cameras, maybe the gain feature. I think that will also change how sensitive the sensor is to the light that it detects. That may increase graininess though.
To be honest, I don't think that will fully solve the problem. Aperture priority mode will automatically set the shutter speed to maintain the correct exposure based on the camera's exposure algorithm. To get clearer video on motion, i.e., when people or cars are moving, you need to have 1. a...
Why don't you open the iris all the way? That will let in more light. Your aperture priority mode is limited the iris opening. What happens if you set it to all the way open.