When Does Google Show Video In SERPS?

I'm doing a lot of video marketing with good success... however... I'm wondering if anyone has any insight as to what causes Google to show video on the first page of the SERPS for a particular niche or keyword.

What seems to be happening to me is: when there is ALREADY a video on the first 1-3 pages of the SERPS, I can easily beat them out and be popped on the first page quickly. However, if there is no video anywhere near the top pages, it becomes very difficult to "break the ice" and bring a video to the first page... with very similar competition.

I'm thinking that there must be some threshold that needs to be met before Google will show video in a niche? It seems that they like to bring a "pair" of videos together in the SERPS... is it possible in some niches I'd have to create 2 videos so that they can move together?

Any insight appreciated...

I found you rank on the first page of Google for the video as a link. Later Google adds a video thumbnail. Then G brings a video pair to the serp.

If there is already a pair, you need to knock out one of the top 2. I found getting to #3 is not so hard for competitive terms. But getting in the top 2 on YT challenging when facing off with old videos.

This is all causal observation. nothing tested or scientific.

Mike, I saw one interesting article about this. This would help you a lot.