Update: This method was always a bit hit and miss. It appears that Viddler has incorporated some “set thumbnail” functionality, see the comment below from Viddler’s Rob Sandie for more details.
Here are the steps to get this working:
1) Get a Viddler API Key by going to http://www.viddler.com/YOUR_VIDDLER_USERNAME/settings/account/
2) Download and install the Viddler PHP wrapper from GitHub
3) Currently, phpviddler does not implement the setThumbnail function, so I’ve created one. Download my setThumbnail function and insert it into the phpviddler.php file you got from GitHub. I put mine just below the setPermalink function.
4) Download my ViddlerSetThumbnail script, rename it to a .php extension, and install it somewhere on your server that is web accessible.
WARNING! If you place this file on your server in a location that is not password protected, anyone who comes upon it in their web browser will be able to change the thumbnails of your videos. Please keep security in mind when using this script.
5) Change the _USERNAME_, _PASSWORD_, and _API_KEY_ defines to those of your Viddler account.
6) If necessary, change the require_once to match where your phpviddler.php file is,
7) Visit the ViddlerSetThumbnail.php script in your web browser, i.e. http://www.YOURSITE.com/PATH/TO/ViddlerSetThumbnail.php
8) The page will load up all the videos in your Viddler account. Below each thumbnail is an input box that lets you set where the thumbnail will be, in seconds, in the video.
9) When a thumbnail is changed, the resulting page will show the thumbnails as returned from Viddler. ALMOST ALWAYS, the thumbnails will be the same as before, as there seems to be a delay for Viddler to process the thumbnail change. DON’T CLICK REFRESH on this page, as it will resubmit the thumbnail change request each time you do. Not a terrible thing, but probably not what you intended. Insted, simply click the “Back to video list” link at the bottom of the page, and refresh every few minutes. You should see that video’s thumbnail change after a few minutes.