functions.php

<?php 

function video($value)
{
	if(preg_match("/youtube/i", $value[1]))
	{
		return ' Youtube: '.$value[1];
	}
	
	if(preg_match("/vimeo/i", $value[1]))
	{
	  return ' Vimeo: '.$value[1];
	}
}

index.php

<?php
require_once 'SimpleShortcode.php';
require_once 'functions.php';

$shortcode = new SimpleShortcode();
$shortcode->addTag('youtube', 'video');
$shortcode->addTag('vimeo', 'video');

$content  = '[youtube]https://www.youtube.com/watch?v=YgHRBEYy6mM[/youtube]';
$content .= '[vimeo]https://vimeo.com/57739087[/vimeo]';
echo $shortcode->apply($content);

SimpleShortcode.php

<?php

class SimpleShortcode
{
	private $tags = [];
	const regex = '/\[%s\](.*?)\[\/%s\]/';
	
	public function __construct($tags = [])
	{
      $this->tags = $tags;	  
	}
	
	public function addTag($tag, $action)
	{
		$this->tags[$tag] = $action;
	}
		
	public function apply($content) 
	{
		foreach($this->tags as $key => $value ) { 
		   $regex    = sprintf(self::regex, $key, $key);
			if(preg_match($regex, $content)) {
			   $content = preg_replace_callback($regex, $value, $content);
			}
		}
		return $content;
	}
}