Filter crossfeed
  Apply headphone crossfeed filter.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
crossfeed AVOptions:
  strength          <double>     ..F.A.... set crossfeed strength (from 0 to 1) (default 0.2)
  range             <double>     ..F.A.... set soundstage wideness (from 0 to 1) (default 0.5)
  level_in          <double>     ..F.A.... set level in (from 0 to 1) (default 0.9)
  level_out         <double>     ..F.A.... set level out (from 0 to 1) (default 1)

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

