If Custom field exist => do that.. If it is not => do something else

I have a code that I use

<?php $key = 'video'; $themeta = get_post_meta($post->ID, $key, TRUE); if($themeta != '') { ?>
<object type="application/x-shockwave-flash" style="width:150px; height:113px;" data="<?php echo get_post_meta($post->ID, 'video', true); ?>">
<param name="wmode" value="opaque" /><param name="movie" value="<?php echo get_post_meta($post->ID, 'video', true); ?>" /></object>
<?php } ?>

So If there is a custom field using video key, it will be displayed. I need to extend this code to display something else when video key is not available. None of my attempts worked well.

Any suggestion is highly appreciated