catch Warning event

[morz]

How do I get warning (ONLY not error) event in libvlc? Example of warning event that I want :
[092fa724] avcodec decoder warning: cannot decode one frame (745 bytes)
[092968ac] faad decoder warning: Maximum number of bitstream elements exceeded

void MainWindow::callback( const libvlc_event_t *ev, void *param )
{
// I want warning event here
}

libvlc_event_attach( em, what_to_pass_here? ,callback, NULL, &_vlcexcep );

Thanks you.