How to get Open Graph Protocol of a webpage by php?

Really simple and well done:

Using https://github.com/scottmac/opengraph

$graph = OpenGraph::fetch('http://www.avessotv.com.br/bastidores-pantene-institute-experience-pg.html');
print_r($graph);

Will return

OpenGraph Object

(
    [_values:OpenGraph:private] => Array
        (
            [type] => article
            [video] => http://www.avessotv.com.br/player/flowplayer/flowplayer-3.2.7.swf?config=%7B%27clip%27%3A%7B%27url%27%3A%27http%3A%2F%2Fwww.avessotv.com.br%2Fmedia%2Fprogramas%2Fpantene.flv%27%7D%7D
            [image] => /wp-content/thumbnails/9025.jpg
            [site_name] => Programa Avesso - Bastidores
            [title] => Bastidores “Pantene Institute Experience†P&G
            [url] => http://www.avessotv.com.br/bastidores-pantene-institute-experience-pg.html
            [description] => Confira os bastidores do Pantene Institute Experience, da Procter & Gamble. www.pantene.com.br Mais imagens:
        )

    [_position:OpenGraph:private] => 0
)

When parsing data from HTML, you really shouldn't use regex. Take a look at the DOMXPath Query function.

Now, the actual code could be :

[EDIT] A better query for XPath was given by Stefan Gehrig, so the code can be shortened to :

libxml_use_internal_errors(true); // Yeah if you are so worried about using @ with warnings
$doc = new DomDocument();
$doc->loadHTML($html);
$xpath = new DOMXPath($doc);
$query = '//*/meta[starts-with(@property, \'og:\')]';
$metas = $xpath->query($query);
$rmetas = array();
foreach ($metas as $meta) {
    $property = $meta->getAttribute('property');
    $content = $meta->getAttribute('content');
    $rmetas[$property] = $content;
}
var_dump($rmetas);

Instead of :

$doc = new DomDocument();
@$doc->loadHTML($html);
$xpath = new DOMXPath($doc);
$query = '//*/meta';
$metas = $xpath->query($query);
$rmetas = array();
foreach ($metas as $meta) {
    $property = $meta->getAttribute('property');
    $content = $meta->getAttribute('content');
    if(!empty($property) && preg_match('#^og:#', $property)) {
        $rmetas[$property] = $content;
    }
}
var_dump($rmetas);