FFmpeg
编译参考：https://cnbin.github.io/blog/2015/05/19/iospei-zhi-ffmpegkuang-jia/
记得要在Build Settings中找到Search Paths，设置Header Search Pahts 和 Library Search Paths如下。不然会报include“libavformat/avformat.h” file not found 错误。
$(SRCROOT)/FFmpeg-iOS/include
/usr/include/libxml2
$(inherited)
$(inherited)
$(PROJECT_DIR)/FFmpegStudying_01/FFmpeg-iOS/lib