Backup Sitecore Media Library items with a PowerShell script

$dataFolder = "C:\inetpub\wwwroot\<YOUR_SITE>\Data"
$mediaLibraryRootPath = "master:/sitecore/media library"

$location = $mediaLibraryRootPath
$dateTime = Get-Date -format "yyyy-MM-d_hhmmss"
$zipName = "Backup Media Library Example"
$zipPath = "$dataFolder/$zipName-$datetime.zip"

function BackupMediaItems {

    [System.Reflection.Assembly]::Load("WindowsBase,Version=3.0.0.0, `
      Culture=neutral, PublicKeyToken=31bf3856ad364e35") | Out-Null

    $ZipPackage=[System.IO.Packaging.ZipPackage]::Open($zipPath, `
      [System.IO.FileMode]::OpenOrCreate, [System.IO.FileAccess]::ReadWrite)

    $items = gci -recurse $sourceDir
    [byte[]]$buff = new-object byte[] 40960

    $items = Get-ChildItem -Path $location -Recurse | 
        Where-Object { $_.TemplateID -ne [Sitecore.TemplateIDs]::MediaFolder }

    $i = 0
    foreach($item in $items) {
            $i = $i + 1
            if([Sitecore.Resources.Media.MediaManager]::HasMediaContent($item))
            {
              Write-Output "$($i). $($item.ItemPath)"

              $mediaItem = New-Object "Sitecore.Data.Items.MediaItem" $item;
              $mediaStream = $mediaItem.GetMediaStream();
              $fileName = Resolve-Path -Path $item.ProviderPath -Relative
              $nm = $item.Name + "." + $item.Extension

              $fileName = "$fileName.$($item.Extension)" `
                -replace "\\","/" -replace "./", "/"
              # Print out the file - the list will show up once the file is downloaded
              "Added: $fileName"

              # Show progress for the operation
              Write-Progress -Activity "Zipping Files " `
                -CurrentOperation "Adding $fileName" `
                -Status "$i out of $($items.Length)" `
                -PercentComplete ($i *100 / $items.Length)

              $partUri = New-Object System.Uri($fileName, [System.UriKind]::Relative)
              $partUri = [System.IO.Packaging.PackUriHelper]::CreatePartUri($partUri);
              $part = $ZipPackage.CreatePart($partUri, `
                "application/zip",  `
                [System.IO.Packaging.CompressionOption]::Maximum)
              $stream=$part.GetStream();

              do {
                $count = $mediaStream.Read($buff, 0, $buff.Length)
                $stream.Write($buff, 0, $count)

              } while ($count -gt 0)

              #Out-Download -Name $nm -InputObject $stream
              $stream.Close()
              $mediaStream.Close()
            }
    }

    $ZipPackage.Close()
}

BackupMediaItems