抓屏，并使用ffmpeg编码成特定格式视屏文件的源代码-Screenshots, and use the source code of ffmpeg encoded into a specific format screen file

mp4封装源代码，代码量少，区别于ffmpeg,mp4_v2,不需要其他任何的第三方库.-mp4 package source code, less code, different ffmpeg, mp4_v2, does not require any other third-party libraries.