Add [this](https://stackoverflow.com/a/51326301) to get the timestamp of the frames dumped. _Corolary_ It's incorrect to assume that by using the `fps` video filter or the `r` flag, the timestamp of the frames is `i/fps` seconds.
Add this to get the timestamp of the frames dumped.
Corolary
It's incorrect to assume that by using the
fpsvideo filter or therflag, the timestamp of the frames isi/fpsseconds.