function wpse_allowedtags() {
    // Add custom tags to this string
        return '<script>,<style>,<br>,<em>,<i>,<ul>,<ol>,<li>,<a>,<p>,<img>,<video>,<audio>'; 
    }

if ( ! function_exists( 'wpse_custom_wp_trim_excerpt' ) ) : 

    function wpse_custom_wp_trim_excerpt($wpse_excerpt) {
    $raw_excerpt = $wpse_excerpt;
        if ( '' == $wpse_excerpt ) {

            $wpse_excerpt = get_the_content('');
            $wpse_excerpt = strip_shortcodes( $wpse_excerpt );
            $wpse_excerpt = apply_filters('the_content', $wpse_excerpt);
            $wpse_excerpt = str_replace(']]>', ']]&gt;', $wpse_excerpt);
            $wpse_excerpt = strip_tags($wpse_excerpt, wpse_allowedtags()); /*IF you need to allow just certain tags. Delete if all tags are allowed */

            //Set the excerpt word count and only break after sentence is complete.
                $excerpt_word_count = 75;
                $excerpt_length = apply_filters('excerpt_length', $excerpt_word_count); 
                $tokens = array();
                $excerptOutput = '';
                $count = 0;

                // Divide the string into tokens; HTML tags, or words, followed by any whitespace
                preg_match_all('/(<[^>]+>|[^<>s]+)s*/u', $wpse_excerpt, $tokens);

                foreach ($tokens[0] as $token) { 

                    if ($count >= $excerpt_length && preg_match('/[,;?.!]s*$/uS', $token)) { 
                    // Limit reached, continue until , ; ? . or ! occur at the end
                        $excerptOutput .= trim($token);
                        break;
                    }

                    // Add words to complete sentence
                    $count++;

                    // Append what's left of the token
                    $excerptOutput .= $token;
                }

            $wpse_excerpt = trim(force_balance_tags($excerptOutput));

                $excerpt_end = ' <a href="'. esc_url( get_permalink() ) . '">' . '&nbsp;&raquo;&nbsp;' . sprintf(__( 'Read more about: %s &nbsp;&raquo;', 'wpse' ), get_the_title()) . '</a>'; 
                $excerpt_more = apply_filters('excerpt_more', ' ' . $excerpt_end); 

                //$pos = strrpos($wpse_excerpt, '</');
                //if ($pos !== false)
                // Inside last HTML tag
                //$wpse_excerpt = substr_replace($wpse_excerpt, $excerpt_end, $pos, 0); /* Add read more next to last word */
                //else
                // After the content
                $wpse_excerpt .= $excerpt_more; /*Add read more in new paragraph */

            return $wpse_excerpt;   

        }
        return apply_filters('wpse_custom_wp_trim_excerpt', $wpse_excerpt, $raw_excerpt);
    }

endif; 

remove_filter('get_the_excerpt', 'wp_trim_excerpt');
add_filter('get_the_excerpt', 'wpse_custom_wp_trim_excerpt');

Post Allowing HTML within WordPress excerpt je prvi puta viđen na bbird.me.