Create A Metabox For A Custom Field

This will create a metabox for you to enter a video code.

    //Creating a MetaBox for Posts to enter Video Code.
add_action('add_meta_boxes','video_meta_box');
function video_meta_box(){
    add_meta_box('video_box_id', 'Enter Video ' , 'video_box_cb','post','normal','default');
}
function video_box_cb($post){
    $value = get_post_meta($post->ID,'video_box',true);

    echo '<textarea rows="4" cols="50" id="video_box", name="video_box">';
        echo $value;
    echo '</textarea>';
}

add_action('save_post','save_video_box');
function save_video_box($post_id){
    $box_data = $_POST['video_box'];
    update_post_meta($post_id,'video_box',$box_data);
}

Use this code to render this code within your theme.

<?php
    $custom_values = get_post_custom($post->ID);
    echo '<p> Video CODE: '.$custom_values['video_box'][0].'</p>';
?>