Where to specify vn option?

With this command line `ffmpeg -i /path/to/video.mp4 -vn '/path/to/audio.wav'`, I can extract audio stream from the video file. After testing ffmpeg-python APIs, I do not find a place to specify the parameter "-vn", though it is working without specifying any args i.e. ```python ffmpeg.input("video.mp4").output("audio.wav") # this code works without a problem, but I want to gain some ideas about ffmpeg-python APIs' logic like how it maps to ffmpeg options. ``` I checked the ffmpeg official docs, `-vn` is under [Video Options](https://ffmpeg.org/ffmpeg.html#Video-Options) section. But I can't find any places, including ffmpeg-python source code, to specify that option. Using filter does not work either, for instance, ``` ffmpeg.input("video.mp4").filter("vn").output("audio.wav") # error: No such filter: 'vn' ``` It is because vn is not a filter. In ffmpeg-python's [examples dir](https://github.com/kkroening/ffmpeg-python/tree/master/examples), there is no video option example either. Where to specify this option to get it work? Thanks