Set an Nginx Bitrate Limit

I run video site, in my Nginx conf i put this code to limit the bandwidth usage:

mp4;
limit_rate 150k;
limit_rate_after 4m;
I would like to setup a dynamic bitrate. For example i could set the dynamic bitrate to 1.2x video file bitrate.

It would provides ability to limit download speed depending on video file bitrate. I would specify a bitrate multiplier ( for example 1.2 )

Or if that's not possible limit rate to 1k after video bitrate for example.

Thanks for your help.

nginx bitrate