mciSendCommand is actually pretty simple. The tricky part is preparing the structure for its fourth argument, since the structure varies based on the second argument.

I imagine it would look like the following:

package MCI;

use strict;
use warnings;

use Encode     qw( decode );
use Win32::API qw( );

use constant {
   # Messages
   MCI_INFO   => 0x80A
   MCI_RECORD => 0x80F,
   ...

   # Flags
   MCI_NOTIFY => 0x01,
   MCI_WAIT   => 0x02,
   ...
};

my $send_command = Win32::API->new(
   'Winmm.dll', 'mciSendCommandW', 'NNNP', 'N',
);

sub send_command {
   my ($device, $msg, $flags, $packed_parms) = @_;
   my $rv = $send_command->Call($device, $msg, $flags, $packed_parms);
   return 1 if $rv == 0;
   die(MCI::Error->new($rv));
}

sub info {
   my ($device, $flags, $win_handle, $max_chars) = @_;
   $max_chars ||= 256;

   my $size = $max_chars * 2;
   my $str_buf = "\0" x $size;

   # MCI_INFO_PARMS
   my $packed_params = pack("IPI",
      $win_handle,
      $str_buf,
      $size,
   );

   return undef if !send_command(
      $device,
      MCI_INFO,
      $flags,
      $packed_params,
   );

   my ($new_size) = unpack("x4x4I", $packed_params);
   return decode('UCS-2le', substr($str_buf, 0, $new_size));  # Or $ne
+w_size-2?
}


sub record {
   my ($device, $flags, $win_handle, $from, $to) = @_;

   # MCI_RECORD_PARMS
   my $packed_params = pack('III',
      $win_handle,
      $from,
      $to,
   );

   return send_command(
      $device,
      MCI_RECORD,
      $flags,
      $packed_params,
   );
}

...

1;
[download]

package MCI::Error;

use strict;
use warnings;

sub new {
   my ($class, $error) = @_;

   my $msg = ...mciGetErrorString...;

   return bless({
      code      => $error & 0xFFFF,
      driver_id => $error >> 16,
      msg       => $msg,
   }, $class);
}

...

1;
[download]

MCIERROR mciSendCommand(
    MCIDEVICEID IDDevice,
    UINT uMsg,
    DWORD_PTR fdwCommand,
    DWORD_PTR dwParam
);

Win32::API->Import("winmm", "mciSendCommand", "NNNN", "N")
  or die $^E;
my $result = mciSendCommand($qux, $quux, $quuux, $quuuux);
[download]

Now, on my Vista 64-bit system, importing that function works and calling it with all-zero parameters does not result in a crash, so we're on the right track. (Though, those DWORD_PTR arguments may need to be of type "P" -- test and see what works).

Hope that helps.

Thanks. I will give it a try.
s/te/ve/