Parse bbcode youtube tag in text and replace with html including the video id

Question

I'm building a blog that should parse bbcode tags like this:

Input: <youtube=http://www.youtube.com/watch?v=VIDEO_ID&feature=channel>
Output:

<object width="400" height="245">
<param name="movie" value="http://www.youtube-    nocookie.com/v/VIDEO_ID&hl=en&fs=1&rel=0&showinfo=0"></param>
<param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param>
<embed src="http://www.youtube-nocookie.com/v/VIDEO_ID&hl=en&fs=1&rel=0&showinfo=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="400" height="245"></embed>
</object>

My function is incredibly simple so far, because I've gotten stuck on the easiest part! Right now, I have a master process function that calls difference process functions. In this case one of them is processYouTubeVideos(). So I call it like so:

$str = eregi_replace('\<youtube=([^>]*)\>', processYouTubeVideos("\\1"), $str);

processYouTubeVideos() receives the URLs from inside the youtube tag perfectly, but for some reason, when using explode() (or split) the delimiter is never found. Even using test values like "u" or "tube"...

function processYouTubeVideos ($str) {

    $params = explode("?", $str);
    $params = explode("&", $params[1]);

    return $params[0];

}

not related to the question, but you might want to look at parse_str() instead of splitting the string yourself — Tom Haigh, May 25 '09 at 22:55
I find this question to be Unclear because there is no declaration of what the desired output is. — mickmackusa, Mar 10 '21 at 15:09

Emil H · Accepted Answer · 2009-05-25T22:04:54.200

Try:

$str = preg_replace('/<youtube=([^>]*)>/e', 'processYouTubeVideos("$1")', $str);

The code that you're attempting to run won't work, because the function on the output string will be called on the target pattern rather than the output. That means that you're sending "\1" literarly to the function. Add var_dump($str); to the beginning of the function and try running your code again, and you'll see this clearly.

preg_replace has a special flag "e" that you can use to execute a function for each time a replacement is made. This works by inserting the subpattern at the marker position ($1) and then running something like eval() or create_function() on the code to execute it and retrieve the result. This then sent back to preg_replace() and the actual replacement is made.

score 0 · Answer 2 · answered Mar 19 '21 at 05:53

Both of the earlier answers are now well and truly deprecated.

The modern technique is to use preg_replace_callback(), then parse the url and isolate the targeted portion of the query string. I'll demonstrate using sprintf() with placeholders in the html template string.

The pattern itself doesn't go to any great effort to validate the bbcode tag, so if you need strong validation, the pattern will need refinement.

Code: (Demo)

$bbCode = <<<BBCODE
Here is some text <youtube=http://www.youtube.com/watch?v=VIDEO_ID&feature=channel> and some more text
BBCODE;

echo preg_replace_callback(
         '~<youtube=([^>]+)>~',
         function ($m) {
             parse_str(parse_url($m[1], PHP_URL_QUERY), $queryStringArray);
             $videoId = $queryStringArray['v'] ?? null;
             if (!$videoId) {
                 return $m[0];  // do not replace bbcode because could not isolate the video id
             }
             return sprintf(
                        '<object width="400" height="245">
                             <param name="movie" value="http://www.youtube-nocookie.com/v/%1$s&hl=en&fs=1&rel=0&showinfo=0"></param>
                             <param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param>
                             <embed src="http://www.youtube-nocookie.com/v/%1$s&hl=en&fs=1&rel=0&showinfo=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="400" height="245"></embed>
                         </object>',
                         $videoId
                    );
         },
         $bbCode
     );

Output:

Here is some text <object width="400" height="245">
                             <param name="movie" value="http://www.youtube-nocookie.com/v/VIDEO_ID&hl=en&fs=1&rel=0&showinfo=0"></param>
                             <param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param>
                             <embed src="http://www.youtube-nocookie.com/v/VIDEO_ID&hl=en&fs=1&rel=0&showinfo=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="400" height="245"></embed>
                         </object> and some more text

score 0 · Answer 3 · answered May 25 '09 at 22:05

The processYouTubeVideos("\1") function is being run before the eregi_replace.

The following does what I believe you intend:

$str = eregi_replace('\<youtube=([^>]*)\>', "\\1", $str);
$str = processYouTubeVideos($str);

It performs the replace, and then sends the resulting value to processYouTubeVideos.

Parse bbcode youtube tag in text and replace with html including the video id

3 Answers3