The issue originates when you have define the "number" parameter on a thumbnail format. When retrieing job record, you will only ever see there is a single thumbnail for that group.

[
        {
            "label": "150_160",
            "number": "30",
            "aspect_mode": "crop",
            "height": "150",
            "width": "160"
        }
]

This comes from the fact that when parsing the thumbnails from the response, you are overwriting the previous thumbnail with the same group label.

In Services_Zencoder_Job

private function _create_thumbnails($thumbnails = array())
{
    foreach($thumbnails as $thumb_attrs) {

        if(!empty($thumb_attrs->group_label)) {
            $this->thumbnails[$thumb_attrs->group_label] = new Services_Zencoder_Thumbnail($thumb_attrs);
        } else {
            $this->thumbnails[] = new Services_Zencoder_Thumbnail($thumb_attrs);
        }
    }
}

The reason why this is a problem is you may need to retrieve the urls for the thumbnails. This will only ever produce a single url, when in fact I should have 30 here.

I'm not sure what the ideal solutions are here.

1. Multi-dimensional array based on group label. This seems convinient, but probably a BC break.
2. No grouping based on label. All thumbnails will be at the same level. This would require more the user to find certain images in their own libraries. I don't think this is a BC break.

Thoughts?