If you use XML feeds to import content into your site or blog you may have experienced the problem that your blogging software or add-on tries to err on the side of caution for security reasons or just messes up the import and in doing so any EMBED or OBJECT tags are stripped in the process.
This is especially annoying when the content is for a blog or news site and the imported content was linking to YouTube videos as it means you have to go through all the posts by hand and reformat the HTML so that the original video is shown.
Luckily even though the actual OBJECT tag gets removed you are usually left with a link to the video on YouTube's site. This can be utilised in a simple regular expression so that you can reformat your content and replace this link with the actual OBJECT HTML.
The regular expression is pretty simple and looks for any anchors pointing to YouTube's site and captures the video ID in a sub group. This sub group is then used in the replace statement as the value for the PARAM and EMBED values that require it.
// use preg_replace to replace anchors with OBJECT/EMBED
// $input is the source HTML
$html = preg_replace("/<a href=\"http:\/\/www\.youtube\.com\/watch\?v=([A-Z1-9]+)\">[\s\S]+?<\/a>/i","<object width=\"425\" height=\"344\"><param name=\"movie\" value=\"http://www.youtube.com/v/$1&hl=en_GB&fs=1&\"></param><param name=\"allowFullScreen\" value=\"true\"></param><param name=\"allowscriptaccess\" value=\"always\"></param><embed src=\"http://www.youtube.com/v/$1&hl=en_GB&fs=1&\" type=\"application/x-shockwave-flash\" allowscriptaccess=\"always\" allowfullscreen=\"true\" width=\"425\" height=\"344\"></embed></object>",$input);
I am using PHP as an example here but the regular expression would be the same across all languages.
Either wrap a call to this function in your own import procedure or if you are using an add-on like Wordpresses WP-o-Matic then you should utilise it in the rewrite section when setting up a new feed import.