Filter abuffer
  Buffer audio frames, and make them accessible to the filterchain.
    Inputs:
        none (source filter)
    Outputs:
       #0: default (audio)
abuffer AVOptions:
  time_base         <rational>   ..F.A.... (from 0 to INT_MAX) (default 0/1)
  sample_rate       <int>        ..F.A.... (from 0 to INT_MAX) (default 0)
  sample_fmt        <sample_fmt> ..F.A.... (default none)
  channel_layout    <string>     ..F.A....
  channels          <int>        ..F.A.... (from 0 to INT_MAX) (default 0)


