Creating bulk posts with Youtube videos

You already have your updateYoutube() function. Edit it to insert a new post. Very generally:

function updateYoutube( $videocode ){
    global $conn;

    $run = $conn->query("SELECT `ID` FROM `youtubetable` WHERE `ID` = '$videocode'");

    if ($run->num_rows > 0)
        return false;
    else
    {
        if ($conn->query("INSERT INTO youtubetable (`ID`) VALUES ('$videocode')") === TRUE) {
          // #################################
          // NOTE: The following 99% cribbed from the wp_insert_post() entry in the Codex
          // Create post object
          $my_post = array(
            'post_title'    => 'My post',
            'post_content'  => $videocode,
            'post_status'   => 'publish',
            'post_author'   => 1,
            'post_category' => array(8,39) // Obviously illustrative only
          );

          // Insert the post into the database
          wp_insert_post( $my_post );
          // ##################################
          return true;
        } else {
            return false;
        }
    }
}

The auto-embedding system should, I believe, take care of the rest, though I have not tested it.