I'm not really sure on how to pass ffmpeg parameters, like changing the audio, hardcoding subtitles etc.

So for example, if I want to add the following ffmpeg options to my transcodings

-vf "ass=subtitles.ass" -c:a aac -pix_fmt yuv420p
How should I add them?

Thanks in advance.

p.s.

Attachment with my current setup.