Filter equalizer
  Apply two-pole peaking equalization (EQ) filter.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
equalizer AVOptions:
  frequency         <double>     ..F.A.... set central frequency (from 0 to 999999) (default 0)
  f                 <double>     ..F.A.... set central frequency (from 0 to 999999) (default 0)
  width_type        <int>        ..F.A.... set filter-width type (from 1 to 5) (default q)
     h                            ..F.A.... Hz
     q                            ..F.A.... Q-Factor
     o                            ..F.A.... octave
     s                            ..F.A.... slope
     k                            ..F.A.... kHz
  t                 <int>        ..F.A.... set filter-width type (from 1 to 5) (default q)
     h                            ..F.A.... Hz
     q                            ..F.A.... Q-Factor
     o                            ..F.A.... octave
     s                            ..F.A.... slope
     k                            ..F.A.... kHz
  width             <double>     ..F.A.... set band-width (from 0 to 99999) (default 1)
  w                 <double>     ..F.A.... set band-width (from 0 to 99999) (default 1)
  gain              <double>     ..F.A.... set gain (from -900 to 900) (default 0)
  g                 <double>     ..F.A.... set gain (from -900 to 900) (default 0)
  channels          <channel_layout> ..F.A.... set channels to filter (default 0xffffffffffffffff)
  c                 <channel_layout> ..F.A.... set channels to filter (default 0xffffffffffffffff)


