Custom Meta Boxes: Store two values in one repeatable field

The serialized array your meta boxes are saving is deformed. I made a few slight changes to your code to get it to work. I created a new post and here is what was saved after being unserialized.

Note: WordPress will automatically unserialize an an array stored in post_meta. Use an online unserializer if you ever want to check the contents.

Array
(
[1] => Array
(
Custom Meta Boxes: Store two values in one repeatable field => Back in Black
[track] => 1
) [2] => Array
(
Custom Meta Boxes: Store two values in one repeatable field => Hells Bells
[track] => 2
) [3] => Array
(
Custom Meta Boxes: Store two values in one repeatable field => Hot for Teacher
[track] => 3
) [4] => Array
(
Custom Meta Boxes: Store two values in one repeatable field => Rack City Bitch
[track] => 4
) 
)

To output this on the front end you just call get_post_meta() and loop through the array.

add_filter( 'the_content', 'get_your_track_meta' );
    function get_your_track_meta( $content ) {
        global $post;
        $metadata = get_post_meta( $post->ID, 'songs', true );
        $content .= '<ul>';
        foreach ( (array) $metadata as $meta) {
            $content .= '<li>' . $meta['title'] . ' -- ' . $meta['track'] . '</li>';
        }
        $content .= '</ul>';
        return $content;
    }

On the front end this gives us a nice unordered list with the track and title:

• Back in Black — 1
• Hells Bells — 2
• Hot for Teacher — 3
• Rack City Bitch — 4

Code Changes:

I had to change your page field to post in you meta box definitions to get it to load on a post and I also moved them inside the add_meta_box function so we wouldn’t have to deal with making them global. In your show box function I cast the get_post_meta variable to an array to get rid of the invalid argument supplied for foreach error I got in Xdebug and fixed your counter.

$songs = get_post_meta( $post->ID, 'songs', true );
        $c = 0;
        if ( count( $songs ) > 0 ) {
            foreach ( (array)$songs as $track ) {
                if ( isset( $track['title'] ) || isset( $track['track'] ) ) {
                    printf( '<p>Song Title <input type="text" name="songs[%1$s]Custom Meta Boxes: Store two values in one repeatable field" value="%2$s" /> -- Track number : <input type="text" name="songs[%1$s][track]" value="%3$s" /><span class="remove">%4$s</span></p>', $c, $track['title'], $track['track'], __( 'Remove Track' ) );
                    $c++;
                }
            }
        }