Comment by lazka

On Windows (so libwinpthread), 8C/16T machine:

  $ flac --version
  flac 1.5.0
  $ hyperfine -r5 "flac -f -8 a.wav a.flac" "flac -j16 -f -8 a.wav a.flac"
  Benchmark 1: flac -f -8 a.wav a.flac
    Time (mean ± σ):     13.148 s ±  0.194 s    [User: 12.758 s, System: 0.361 s]
    Range (min … max):   12.934 s … 13.318 s    5 runs

  Benchmark 2: flac -j16 -f -8 a.wav a.flac
    Time (mean ± σ):      2.404 s ±  0.012 s    [User: 14.126 s, System: 1.355 s]
    Range (min … max):    2.395 s …  2.425 s    5 runs

  Summary
    flac -j16 -f -8 a.wav a.flac ran
      5.47 ± 0.09 times faster than flac -f -8 a.wav a.flac