PowerShell script to use 7-Zip in order to compress a directory quickly by not attempting to recompress filetypes (like ZIP files) that are already compressed. These filetypes are included in the resulting archive by using the "store" method which skips compression for those files. All other filetypes are compressed like normal.

7Zip_CompressDirButUseStoreBasedOnExtension.ps1

#REQUIRED: set the directory you want to compress.
$dirToArchive = "C:\path\to\dir\"

#leave blank in order to automatically use directory name as archive name, otherwise enter the filename of the archive to create
$archiveName = ""
#$archiveName = "Data.7z"

#path to 7z.exe
$exec = "C:\Program Files\7-Zip\7z.exe"

if ([string]::IsNullOrWhiteSpace($archiveName) )
{
    $archiveName = (split-path -leaf $dirToArchive)+".7z"
}
$papadir = (Get-Item $dirToArchive ).Parent.FullName
#archive is automatically put into parent directory of $dirToArchive 
$archiveName = Join-Path $papadir $archiveName

echo "Archive Path: $archiveName"

if (Test-Path "$archiveName")
{  
    echo "archive already exists"
    exit
    #del "$archiveName"
}

$pw = Read-Host 'Password? Leave Blank to Not Use Encryption.'

$extList = get-childitem -r "$dirToArchive" | where Attributes -NotMatch "Directory" | %{$_.Extension.ToLower()} | select -unique | sort
#loop through set of unique file extensions found in dir and add each one to archive (compressing or not compressing based on the extesnsion)
Foreach ($i in $extList)
{
    $str = $i.ToString()
    #change default compression level here (5=normal)
    $m = 5
    #for following extensions, Store but do not compress
    if ($str -in (".zip", ".7z", ".rar", ".gz", ".bz2", ".pdf", ".docx", ".accdb", ".xlsx", ".png", ".jpg", ".avi", ".mpg", ".mp3", ".m4v", ".m4a"))
    {
        $m = 0
    }

    echo "Ext: $str m = $m" 
    
    $strWithExt = join-path "$dirToArchive" "*$str"
    $AllArgs = @('a', "-mx=$m", """$archiveName""", """$strWithExt""", "-r")
    #only add password param if user actually specified a password
    if ($pw -And $pw.Trim().Length -gt 0)
    {
        $AllArgs += "-p$pw"
    }

    & "$exec"  $AllArgs 
}