OG:Audio facebook meta tags

You are probably using this code in your theme’s header.php. When this file is loaded $post is not available yet (it’ll be inside the Loop). So you’d need to declare before anything global $post;.

But that’s not the best approach. If you swap themes, what? Do it again?
See: Where to put my code: plugin or functions.php?

With the following plugin, we will hook into wp_head and print our meta based on some Conditional Tags:

<?php
/* Plugin Name: Print Audio OG */

add_action( 'wp_head', 'print_audio_og_wpse_99152', 0 );

function print_audio_og_wpse_99152()
{
    // Print only in single posts or pages
    if( is_single() || is_page() )
    {
        global $post;
        $meta_value = get_post_meta( $post->ID, 'meta_audio_attachment', true );
        if( $meta_value )
            echo "
<meta property='og:audio' content="$meta_value" />
<meta property='og:audio:title' content="$post->post_title" />
<meta property='og:audio:artist' content="Test" />
<meta property='og:audio:album' content="Test Album" />
<meta property='og:audio:type' content="application/mp3" />
";
    }
}

You’ll have to adapt get_post_meta.
Increase the hook priority, now 0 (zero), to move the insertion point in the rendered HTML.

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