To help Google index your videos effectively, use a single, unique, and stable URL for each video thumbnail. Avoid using URLs that expire quickly or change frequently, as this can prevent Google from accessing the thumbnail and hinder your video's eligibility for video features. Stable thumbnail URLs ensure consistent availability to Googlebot and Googlebot Images, improving your video's chances of appearing in video search results and rich features. Additionally, make sure the thumbnail file is accessible without restrictions such as robots.txt or login requirements. [Google]