Google has video SEO documentation to vastly clarify the video indexing criteria and technical requirements. Plus, Google added a new watch page section to the document and expanded the examples in the document.
There are a ton of changes to the document, if you want to compare both, you can compare:
I think Google made these changes because of the confusion around the video mode changes to when Google shows a video thumbnail in the search results.
The new indexing criteria says:
To be eligible for video features, a video must meet the following indexing requirements:
- The watch page must be indexed.
- The indexed watch page must be performing well in Search before its video can be considered for indexing. Just because the watch page is indexed doesn’t mean that the video will also be indexed.
- The video must be embedded on a watch page.
- The video can’t be hidden behind other elements. If you’re using a paywall (for example, users need to sign in or subscribe before seeing the video), add paywall structured data so that Google can still find and index the video.
