HTML embed video using PHP variable doesn't work

I'm trying to display all videos a webpage using the following code, I've gotten as far as being able to iterate over the files, printing the file names and embedding a video. However the videos are greyed out and don't work, I suspect I did something wrong with using $filename in the code.

<?php
$dir = new DirectoryIterator(dirname(__FILE__));
foreach ($dir as $filename) {
    if (!$filename->isDot()) {

        if ($filename != "index.php" and $filename != "error_log") {

            echo $filename, "<br>"; 

            echo '<video width="400" controls="controls" preload="metadata">
            <source src=$filename type="video/mp4"></video>';

            echo "<br><br>";
        }

    }
}
?>

This is how it shows up: