插件说明：
https://docs.nvidia.com/metropolis/deepstream/dev-guide/text/DS_plugin_gst-nvdsosd.html
python开发中插件参数：
https://docs.nvidia.com/metropolis/deepstream/python-api/index.html
举例说明：
osd插件中text-bg-color的参数含义：
red – float, Holds red component of color. Value must be in the range 0-1. green – float, Holds green component of color. Value must be in the range 0-1. blue – float, Holds blue component of color. Value must be in the range 0-1. alpha – float, Holds alpha component of color. Value must be in the range 0-1.
透明化设置：
[osd] enable=1 gpu-id=0 border-width=1 text-size=15 text-color=1;0;0;1; text-bg-color=0.3;0.3;0.3;0 font=Serif show-clock=0 clock-x-offset=800 clock-y-offset=820 clock-text-size=12 clock-color=1;0;0;0 nvbuf-memory-type=0
