param(
    [Parameter(Mandatory=$true)]
    [ValidateSet("play_pause","next","prev","stop")]
    [string]$Action
)

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

$vk = switch ($Action) {
    "play_pause" { 0xB3 }
    "next"       { 0xB0 }
    "prev"       { 0xB1 }
    "stop"       { 0xB2 }
}

[Win32.MediaKey]::keybd_event($vk, 0, 0, [UIntPtr]::Zero)
[Win32.MediaKey]::keybd_event($vk, 0, 2, [UIntPtr]::Zero)