基本使用命令
ffmpeg -i input.mp4 output.avi //视频格式转换
ffmepg -i input.mp4 -r fps image%3d.jpg //视频转成图片
//fps is num of picture per second;
//%3d will generate picture named three digit num
ffmpeg -video_size 1920x1080 -framerate 25 -f x11grab -i :0.0+0,0 output.avi //用ffmpeg抓屏
//This will grab the image from desktop, starting with the upper-left corner at (x=100, y=200) with the width and height of 1024x768