Wordpress get_posts() not returning all posts with post_type=attachment

Question

I am trying to get a list of all videos from Wordpress' media library. I do it from outside the regular WP loop, hence including wp-load.php. However, I get returned 0 posts with this code (though there are actually 4 videos):

include('../../../wp-load.php');

$args = array( 
  'post_type' => 'attachment', 
  'post_mime_type' => 'video', 
  'numberposts' => -1, 
  'posts_per_page'=>-1, 
  'suppress_filters' => true, 
  'post_status' => 'any', 
  'post_parent' => null
); 
$attachments = get_posts( $args );
echo(count($attachments));
if ( $attachments ) {
    foreach ( $attachments as $post ) {
        setup_postdata( $post );
        the_title();
        echo('<br />');
        echo wp_get_attachment_url( $post->ID, false );
        echo('<br /><br />');
    }
    wp_reset_postdata();
}

However, the issue does not seem to be related to the videos directly (or only): If I remove the 'post_mime_type' => 'video' argument from the query, I get returned only 16 instead of 121 total attachments (images, sounds, videos) in my media library. I am really starting to lose my mind on this issue...

Answer 1

Heureka! After hours of trying out nearly everything I found the cause of this issue: the plugin Polylang.

Long story short, if Polylang is installed in your Wordpress installation, one seems to have to provide another argument for the get_posts() function: it's called lang!

It can be an empty string to list simply all assets, or one of the specific language tags used by Polylang in the specific Wordpress installation. So the finally working code must look like this:

include('../../../wp-load.php');

$args = array('lang' => '', 'post_type' => 'attachment', 'post_mime_type' => 'video', 'numberposts' => -1, 'posts_per_page'=>-1, 'suppress_filters' => true, 'post_status' => 'any', 'post_parent' => null); 
$attachments = get_posts( $args );
echo(count($attachments));
if ( $attachments ) {
    foreach ( $attachments as $post ) {
        setup_postdata( $post );
        the_title();
        echo('<br />');
        echo wp_get_attachment_url( $post->ID, false );
        echo('<br />');echo('<br />');
    }
    wp_reset_postdata();
}

I really hope this can help somebody else save some valuable time!

This link helped in finding my solution: http://polylang.wordpress.com/documentation/documentation-for-developers/general/