Google made a small update to the video structured data help documents to communicate that the thumbnailUrl now also supports WebP and SVG image formats, in addition to the already documented BMP, GIF, JPEG, and PNG image formats.
Google wrote that on April 7, 2021 it "updated the Video structured data documentation to state that the thumbnailUrl property must use one of the supported Google Images file formats. Previously, the documentation didn't include WebP and SVG."
You can now see for the thumbnail-url section of the video structured data page links to the thumbnail image guidelines, that now specifies the supported thumbnail formats are from the Google Images supported formats. Yes, that is a lot of links. But that document says "Google Images supports images in the following formats: BMP, GIF, JPEG, PNG, WebP, and SVG."
This is what sample code looks like for the thumbnailUrl and keep in mind, the .jpg can now be webp or svg:
Forum discussion at Twitter.
