原因可能是您VideoCapture设备未配置更高的帧速率，或者根本不支持更高的帧速率.

The reason may be that you VideoCapture device is not configured for higher framerate or it does not support higher framerate at all.

您指定了非常低的帧频，我不知道这对您意味着什么，但是我用2台相机对其进行了测试.通过稍微修改代码，我可以将第一台摄像机的最大速度提高到15fps，但是第二台摄像机以25fps的速度运行而没有问题.这些是我的预期数字.

You specified very low frame rate, I don't know what this means to you, but I tested it with my 2 cameras. With slightly modified code, I can max out the first camera to 15fps, but the second one is running at 25fps without problems. These are expected numbers for me.