From your array, you should get the Media ID of the videos. If you have the media ID, it will be as listed below:
// Let's say you have the media ID
$meta = filesize( get_attached_file( $attachment_id ) );
By using the size format function you can list the size
echo size_format($meta);
Update according to your updated case scenario:
$custom_field_value="8785,8786,8787"; //If your custom field contains the IDs like this, simply replace my text with the custom field
if (!empty($custom_field_value)) {
$media_ids = explode(',', $custom_field_value);
if ($media_ids) {
echo '<ul>';
foreach ($media_ids as $media_id) {
$file_size = size_format(filesize( get_attached_file( $media_id ) ));
echo '<li>'.get_the_title($media_id).' - '.$file_size.'</li>';
}
echo '</ul>';
}
}
Results:
