Filter axcorrelate
  Cross-correlate two audio streams.
    Inputs:
       #0: axcorrelate0 (audio)
       #1: axcorrelate1 (audio)
    Outputs:
       #0: default (audio)
axcorrelate AVOptions:
  size              <int>        ..F.A..... set segment size (from 2 to 131072) (default 256)
  algo              <int>        ..F.A..... set alghorithm (from 0 to 1) (default slow)
     slow            0            ..F.A..... slow algorithm
     fast            1            ..F.A..... fast algorithm


