utilizing media_sideload_image with a file from theme listing

I am constructing a WordPress web site through which an admin can add a video file from put up metabox.

After that put up is saved and the video file is hooked up to the put up, I used ffmpeg to get the screenshot on the first second of video, then save this screenshot as a JPG file in ‘tmp’ listing in theme listing.

Lastly, I wish to programmatically make this screenshot as put up featured picture. I exploit media_sideload_image perform, which usually be used to get picture from one other server and set that picture as put up featured picture and I feel this perform could possibly be used on this case additionally.

In my case, the video screenshot was efficiently saved to ‘tmp’ listing in my theme dir, however the media_sideload_image half didn’t return something for additional course of. Here is my perform:

perform create_video_featured_image($post_id, $image_uri) {

// $image_uri = 'http://localhost/demo-site/wp-content/themes/mytheme/tmp/video_thumb_952.jpg';
$media = media_sideload_image($image_uri, $post_id);

if(!empty($media) && !is_wp_error($media)){
    $args = array(
        'post_type' => 'attachment',
        'posts_per_page' => -1,
        'post_status' => 'any',
        'post_parent' => $post_id
    );

    // reference new picture to set as featured
    $attachments = get_posts($args);

    if(isset($attachments) && is_array($attachments)){
        foreach($attachments as $attachment){
            // seize supply of full dimension photographs (so no 300x150 nonsense in path)
            $picture = wp_get_attachment_image_src($attachment->ID, 'full');
            // decide if within the $media picture we created, the string of the URL exists
            if(strpos($media, $picture[0]) !== false){
                // in that case, we discovered our picture. set it as thumbnail
                set_post_thumbnail($post_id, $attachment->ID);
                // solely need one picture
                break;
            }
        }
    }
}
}

Am I lacking something or is there one other technique to work round on this case ?

Thanks very a lot !