One of the questions asked during Semantic Mastery's Hump Day Hangouts episode 83 was about fixing videos showing in search engine results page that have no thumbnails.
The exact question was:
And if I can be cheeky and ask one more quick one, do you ever have videos on the 1st page with no thumbnail? I have one there with just a black screen, but for another keyword, the same video on page 2 shows my thumbnail? Very weird, is there a way to fix this??