Can I deduce the filesize from the other specs of a x264 file?

[bruno321]

I want to understand what exactly determines file size in a x264 encode, and I haven't managed to find this info.

For example, suppose I gave you the full Mediainfo output of a x264 video in mkv container, minus the file size. Is there a formula that allows me to deduce it from the given data?

[sneaker_ger]

filesize = bitrate * duration

Other than that: no, there is no formula to figure this out. You can run the exact same x264 settings on 2 different 90 minute movies and end up with 2 differently sized files (except if you use --bitrate instead of --crf, of course.). Compressibility is content dependent.