How to add option vsync or fps_mode?

[Pandede]

Question

Is there any method to modify the option of vsync or fps_mode?
Here is the FFMPEG documentation (the option -vsync or -fps_mode).

Attempts

I've tried to pass the option with dict but it does not seem to work.

output_ctn = av.open('rtmp://path/to/rtmp/server', 'w', format='flv', options={'fps_mode': 'cfr'})

Similar Issues

I found the duplicate issue #225 but it does not have any answer in it.