Incrementally rename files for ffmpeg

incremental_rename.ps1

$prefix="frame_"
$files = Get-ChildItem "<Path where the pngs are>" -Filter *.png | Sort-Object
$fileCount = 0
$files | 
Foreach-Object {
    $fileCount++
    $currentFileNumber = [int]$_.BaseName.Substring($prefix.Length)
    if ($currentFileNumber -ne $fileCount) {
        $newFileFormat = "$prefix{0:d4}.png" -f $fileCount 
        Rename-Item $_.FullName $newFileFormat 
        Write-Output "$newFileFormat (renamed)"
    }
    else {
        $orig = $_.Name + " (orig)"
        Write-Output $orig
    }
}

Write-Output "Done"