Get-ChildItem -Filter *.mkv | ForEach-Object {
  $out = "$($_.BaseName)_clean.mkv"
  if (Test-Path $out) { return }

  ffmpeg -i "$($_.FullName)" `
    -map 0 `
    -map_metadata -1 `
    -map_chapters -1 `
    -c copy `
    "$out"
}