preg-match-all - preg_match_all 用结束词解析问题

Question

$content = '<!--title:FAST-->
<iframe src="https://example.com/38d6996f11" width="600" height="400" frameborder="0" scrolling="no" allowfullscreen="true" webkitallowfullscreen="true" mozallowfullscreen="true"></iframe>
asd
<!--nextpage--><!--title:FEM-->
<iframe src="https://example.com/38d6996f11" width="600" height="400" frameborder="0" scrolling="no" allowfullscreen="true" webkitallowfullscreen="true" mozallowfullscreen="true"></iframe>

<!--nextpage--><!--title:DRIVE-->
<iframe src="https://example.com/38d6996f11" width="600" height="400" frameborder="0" scrolling="no" allowfullscreen="true" webkitallowfullscreen="true" mozallowfullscreen="true"></iframe>

<!--nextpage--><!--title:MOLY-->
<iframe src="https://example.com/38d6996f11" width="600" height="400" frameborder="0" scrolling="no" allowfullscreen="true" webkitallowfullscreen="true" mozallowfullscreen="true"></iframe>

qwe';

preg_match_all('@<!--title:(.*?)-->(.*?)(?<!--nextpage)@is', $content, $content_out, PREG_PATTERN_ORDER);

echo '<pre>';
print_r($content_out);

我对这个 preg_match_all 正则表达式有疑问，这段代码只给出了三个部分。我需要它们（四个部分用词；不仅仅是 iframe），有人可以帮忙吗？