Wordpress: Responsive image embedding

/**
 * Modify markup of inline images added via the visual editor
 * to follow the srcset responsive image pattern
 * @param  string $html  original image markup
 * @param  int    $id    attachment ID
 * @param  string $alt   alt text 
 * @param  string $title image title
 * @return string        modified markup
 */
function responsive_image_embed( $html, $id, $alt, $title ) {
    $sizes = array(
        'thumbnail',
        'medium',
        'large',
        'full'
    );

    $fallback = wp_get_attachment_image_src( $id, 'medium' );

    $attributes = array( 
        'alt' => $alt,
        'title' => $title,
        'src' => $fallback[0],
        'class' => 'inline-image'
    );

    $html = '';
    $html .= '<img';

    $html .= ' srcset="';

    foreach( $sizes as $size ) {
        $src = wp_get_attachment_image_src( $id, $size );
        $html .= $src[0] . ' ' . $src[1] . 'w,';
    }

    $html = rtrim( $html, ',' );

    $html .= '"';

    foreach( $attributes as $attribute => $value ) {
        $html .= ' ' . $attribute . '="' . esc_attr( $value ) . '"';
    }    

    $html .= '>';

    return $html;
}

add_filter( 'get_image_tag', 'responsive_image_embed', 10, 4 );