[FFmpeg-user] What does "-vol" parameter mean in ffmpeg?

[littlebat]

Hi,

I can't understand how to use "-vol" parameter to increase volume in
ffmpeg. I know "-vol 256" mean keep volume unchanged. But I don't know
how to choose a proper number for a video file to increase volume. For
example, does "-vol 512" mean volume intensity is twice as original
file? ( volume intensity:
http://en.wikipedia.org/wiki/Decibel#Power_quantities )

thanks.

littlebat