Filter volume
  Change input volume.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
volume AVOptions:
  volume            <string>     ..F.A... set volume adjustment expression (default "1.0")
  precision         <int>        ..F.A... select mathematical precision (from 0 to 2) (default float)
     fixed                        ..F.A... select 8-bit fixed-point
     float                        ..F.A... select 32-bit floating-point
     double                       ..F.A... select 64-bit floating-point
  eval              <int>        ..F.A... specify when to evaluate expressions (from 0 to 1) (default once)
     once                         ..F.A... eval volume expression once
     frame                        ..F.A... eval volume expression per-frame
  replaygain        <int>        ..F.A... Apply replaygain side data when present (from 0 to 3) (default drop)
     drop                         ..F.A... replaygain side data is dropped
     ignore                       ..F.A... replaygain side data is ignored
     track                        ..F.A... track gain is preferred
     album                        ..F.A... album gain is preferred
  replaygain_preamp <double>     ..F.A... Apply replaygain pre-amplification (from -15 to 15) (default 0)
  replaygain_noclip <boolean>    ..F.A... Apply replaygain clipping prevention (default true)

This filter has support for timeline through the 'enable' option.

