Filter biquad
  Apply a biquad IIR filter with the given coefficients.
    slice threading supported
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
biquad AVOptions:
  a0                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 1)
  a1                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 0)
  a2                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 0)
  b0                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 0)
  b1                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 0)
  b2                <double>     ..F.A.... (from INT_MIN to INT_MAX) (default 0)
  mix               <double>     ..F.A.... set mix (from 0 to 1) (default 1)
  m                 <double>     ..F.A.... set mix (from 0 to 1) (default 1)
  channels          <channel_layout> ..F.A.... set channels to filter (default 0xffffffffffffffff)
  c                 <channel_layout> ..F.A.... set channels to filter (default 0xffffffffffffffff)

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

