ffmpeg

https://www.cleancss.com/explain-command/ffmpeg/6905

scale2ref

filter
Scale (resize) the input video, based on a reference video.

psnr

ssim

-shortest (output)

Finish encoding when the shortest input stream ends.

-an

The -vn / -an / -sn / -dn options can be used to skip inclusion of video, audio, subtitle and data streams respectively, whether manually mapped or automatically selected, except for those streams which are outputs of complex filtergraphs.

-f fmt (input/output)

Force input or output file format. The format is normally auto detected for input files and guessed from the file extension for output files, so this option is not needed in most cases.

dev/null

在类Unix系统中，/dev/null，或称空设备，是一个特殊的设备文件，它丢弃一切写入其中的数据（但报告写入操作成功），读取它则会立即得到一个EOF。