$content = get_the_content();
// regex (fixed) replacing '<embed>' with '(embed )'
$content = preg_replace("/<embed?[^>]+>/i", "(embed) ", $content);
// remove all tags
$content = wp_strip_all_tags($content);
Edited according to the first comment:
What you are trying to remove are not tags, these are HTML character entities. E. g.,
<p> was converted to
<p> by WordPress when you've saved the content in the visual editor.
You have two choices:
- edit the content in the built-in text editor to remove those entities (switch the editor from Visual to HTML mode);
- use different regexes to remove entities after the post was fetched.
For example (not tested, but you have the idea):
$content = preg_replace("/<embed?[.]+>/i", "(embed) ", $content);
$content = preg_replace("/<[.]+>/i", "", $content);