Ffmpeg-quality-metrics

* Update readme, fixes 18.

* Merge pull request 16 from dpasqualin/issue_15.

Closes 15: fix 'print_stderr' is not defined

* Closes 15: fix 'print_stderr' is not defined.

* Improve readme.

* Improve warnings and messages, add -r parameter.

* Merge pull request 14 from BassThatHertz/master.

Prevent users on Windows from seeing an "UnboundLocalError"

* Add sys.exit(1) to prevent users on Windows from seeing "UnboundLocalError: local variable 'model_path' referenced before assignment"

* Set PTS and framerate for input files.

* Apply black formatting.

* Add global statistics, fixes 13.