说明：  摄像功能：按键1 调用tracer程序实现摄像功能 录音放音功能：按键3 开启录音 调用sound程序启动录音放音功能 拍照功能：按键2 调用video程序完成照片的拍摄与存储 退出：按键6 通过对子进程的控制 可以退出程序 实现上述三种功能之间的转换
(Camera: Press 1 to call tracer program to achieve functional imaging Recording and playback function: Key 3 open calls sound recording program starts recording and playback functions Camera features: call button 2 video program is completed the photo shoot and storage Exit: Key 6 by controlling the sub-process can exit the program to achieve the conversion between these three functions)