Filter surround
  Apply audio surround upmix filter.
    slice threading supported
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
surround AVOptions:
  chl_out           <string>     ..F.A.... set output channel layout (default "5.1")
  chl_in            <string>     ..F.A.... set input channel layout (default "stereo")
  level_in          <float>      ..F.A.... set input level (from 0 to 10) (default 1)
  level_out         <float>      ..F.A.... set output level (from 0 to 10) (default 1)
  lfe               <boolean>    ..F.A.... output LFE (default true)
  lfe_low           <int>        ..F.A.... LFE low cut off (from 0 to 256) (default 128)
  lfe_high          <int>        ..F.A.... LFE high cut off (from 0 to 512) (default 256)
  fc_in             <float>      ..F.A.... set front center channel input level (from 0 to 10) (default 1)
  fc_out            <float>      ..F.A.... set front center channel output level (from 0 to 10) (default 1)
  lfe_in            <float>      ..F.A.... set lfe channel input level (from 0 to 10) (default 1)
  lfe_out           <float>      ..F.A.... set lfe channel output level (from 0 to 10) (default 1)


