PowerShell script to run mkvmerge on all mkv and mp4 files in a directory, supports all mkvmerge parameters. Creates new mkv files in "mkvmerge" subdirectory of current folder without overwriting or deleting the originals.

Start-MkvmergeCurrentFolder.ps1

$parameters = Read-Host "Enter parameters, leave blank for defaults"
$parameterArray = $parameters.Split(" ")
Write-Host "For single subtitle, base name must match video file name (without extension).`nIf files have multiple external subtitles, they must be named like so: videoFileName_Track[0 - 99].[ext]"
$numSubs = Read-Host "Number of external subtitles to merge? (0 for none)"
if ($numSubs -gt 0) {
    Write-Host "External subtitles:`n`tass,pgs,vobsub,srt,etc."
    $subsExt = Read-Host "Subtitle file type?"
}
$subsName = @()

Get-ChildItem -Path '*.mkv', '*.mp4' | ForEach-Object {

    Write-Verbose "Processing file: $_"
    $mkvFullName = [System.IO.Path]::ChangeExtension($_.FullName, "mkv")
    $mkvFileName = [System.IO.Path]::GetFileName($mkvFullName)
    $mkvBaseNameNoExt = [System.IO.Path]::GetFileNameWithoutExtension($_.FullName)

    if ($numSubs -gt 1) {
        for ($i = 0; $i -lt $numSubs; $i++) {
            $subsName = $subsName + "$mkvBaseNameNoExt`_Track$i.$subsExt"
        }
    }
    elseif ($numSubs -eq 1) {
        $subsName = "$mkvBaseNameNoExt.$subsExt"
    }

    & mkvmerge -o ".\mkvmerge\$mkvFileName" $parameterArray $_.FullName $subsName
}