音视频合成相关
https://www.jianshu.com/p/868e8ee65a95
https://www.jianshu.com/p/b8782cc09e52
附:视频时间戳定义理解 https://stackoverflow.com/questions/4001755/trying-to-understand-cmtime-and-cmtimemake
https://www.jianshu.com/p/868e8ee65a95
https://www.jianshu.com/p/b8782cc09e52
附:视频时间戳定义理解 https://stackoverflow.com/questions/4001755/trying-to-understand-cmtime-and-cmtimemake