Handbreak script example

$filesToConvert = Get-ChildItem -Path "mkv folder" -file -Recurse
$outputPath = "c:\outputfolder\"

$handbreak = get-item -path "path to handbreak.exe"

foreach ($file in $filesToConvert){
    $output = "$($outputPath)$($file.BaseName).mp4"
    Start-Process -FilePath $handbreak.FullName -ArgumentList "-i $($file.FullName) -o $($output)"
}