Google has made improvements to their Search Console video indexing report, adding more details on why “Google could not determine the prominent video on the page”. This is in order to help site owners, developers, content creators, etc. understand the issue better by providing more actionable reasons and what could be done to resolve them.
According to Google, the main reason why Google does not index a video on a page is because they could not identify a prominent enough video to qualify as the video for the page. The improvement to reporting added these three specific reasons and what could be done to resolve the issue and make the video eligible for indexing.
Note that the search console video indexing report shows 3 months of historical data. Due to this, you may still see the “Google could not determine the prominent video on the page” in the list of reason in the Video Indexing report, but it has no effect on your pages. The new reasons will also appear when applicable while inspecting a specific video page URL.
Check out the search central blog on this for more details.