plugin.php

<?php
function mlbtv_shortcode( $attr, $content = '' ) {
    $attr = shortcode_atts( array(
        'id' => null,
        'width' => 400,
        'height' => 224,
    ), $attr );

    $attr = array_map( 'absint', $attr );
    $url = add_query_arg( array(
        'content_id' => $attr['id'],
        'width' => $attr['width'],
        'height' => $attr['height'],
        'property' => 'mlb',
    ), 'http://wapc.mlb.com/shared/video/embed/embed.html' );

    return sprintf( '<iframe src="%s" width="%d" height="%d" frameborder="0">Your browser does not support iframes.</iframe>', esc_url( $url ), $attr['width'], $attr['height'] );
}
add_shortcode( 'mlbtv', 'mlbtv_shortcode' );