This PowerShell script process sets the selected audio track (1 or 2) to default in all dual audio MKV-files in a directory

mkvpropedit-dual-audio.ps1

#COPYRIGHT: Gabriel Smoljar (2013)
#WEBSITE: http://twitter.com/gabbsmo
#DESCRIPTION: This PowerShell script process sets the selected audio track (1 or 2)
#             to default in all dual audio MKV-files in a directory
#
#NOTES: MKVPropEdit must be added to PATH for this script to work.
#DEPENDENCIES: MKVPropEdit (included in MKVToolNix http://www.bunkus.org/videotools/mkvtoolnix/)
Param(
    [parameter(Mandatory=$true)]
    [alias("i")]
    $InputDir,
    [parameter(Mandatory=$true)]
    [alias("a")]
    $Audio)
    
$items = Get-ChildItem -Path $InputDir

foreach ($item in $items)
{
    if ($items.Attributes -ne "Directory")
    {
        $InputFile = $InputDir + "\" + $item.name
        
        if ($item.Extension -ieq ".mkv")
        {
            if ($Audio -ieq "1")
            {
                mkvpropedit $InputFile --edit "track:a1" --set "flag-default=1" --edit "track:a2" --set "flag-default=0"
            }
            if ($Audio -ieq "2")
            {
                mkvpropedit $InputFile --edit "track:a1" --set "flag-default=0" --edit "track:a2" --set "flag-default=1"
            }
        }
    }
}