param(
    [Parameter(Mandatory=$true)]
    [ValidateSet("up","down","mute","max")]
    [string]$Action,

    [int]$Times = 1
)

Add-Type -Name VolumeKey -Namespace Win32 -MemberDefinition @'
[DllImport("user32.dll")]
public static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, System.UIntPtr dwExtraInfo);
'@

$KEY_UP   = 0xAF
$KEY_DOWN = 0xAE
$KEY_MUTE = 0xAD

$vk = switch ($Action) {
    "up"   { $KEY_UP }
    "down" { $KEY_DOWN }
    "mute" { $KEY_MUTE }
    "max"  { $KEY_UP }
}

$count = if ($Action -eq "max") { 50 } else { $Times }

for ($i = 0; $i -lt $count; $i++) {
    [Win32.VolumeKey]::keybd_event($vk, 0, 0, [UIntPtr]::Zero)
    [Win32.VolumeKey]::keybd_event($vk, 0, 2, [UIntPtr]::Zero)
    Start-Sleep -Milliseconds 25
}