Inserting echo inside echo on php

Question

I try to call an echo inside the shortcode. The line of code is like this:

<?php echo do_shortcode('[audio src="<?php echo $audio; ?>"]'); ?>

The complete code is like this:

<?php if(get_post_meta($post->ID, '_format_audio_embed', true)!=''){ 
    $audio = get_post_meta($post->ID, '_format_audio_embed', true);
} else {
    $audio = '';    
}
?></h1>  

<?php echo do_shortcode('[audio src="<?php echo $audio; ?>"]'); ?>

My code did not work. Am I missing something?

Answer 1

Why are you using PHP inside PHP? Try to concat:

<?php echo do_shortcode('[audio src="'.$audio.'"]'); ?>