Filter biquad
  Apply a biquad IIR filter with the given coefficients.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
biquad AVOptions:
  a0                <double>     ..F.A... (from -32768 to 32767) (default 1)
  a1                <double>     ..F.A... (from -32768 to 32767) (default 1)
  a2                <double>     ..F.A... (from -32768 to 32767) (default 1)
  b0                <double>     ..F.A... (from -32768 to 32767) (default 1)
  b1                <double>     ..F.A... (from -32768 to 32767) (default 1)
  b2                <double>     ..F.A... (from -32768 to 32767) (default 1)


