The original code was non-working because the notication was never
setup correctly and resulted in a DSERR_INVALIDCALL. A proper fix
would look like:

         if( sys->p_notify )
         {
+            IDirectSoundBuffer_Stop( aout->sys->p_dsbuffer );
             DSBPOSITIONNOTIFY notif = {.dwOffset = aout->sys->i_write, .hEventNotify = sys->hnotify_evt } ;
             if( IDirectSoundNotify_SetNotificationPositions( sys->p_notify, 1, &notif ) ==  DS_OK )
             {
+                IDirectSoundBuffer_Play( aout->sys->p_dsbuffer, 0, 0, DSBPLAY_LOOPING );
                 WaitForSingleObject( sys->hnotify_evt, INFINITE );
                 IDirectSoundBuffer_Stop( aout->sys->p_dsbuffer );
             }

But fixing it makes the problem worse since the notification is setup
too late and thus the buffer will replay a full loop of the back
buffer during a drain.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>