Select poster image given player size
When calling `setup` on a JWPlayer instance, we can provide the url for our "poster image" that's displayed before the video plays. We can provide to this field any of the poster images generated using the poster image tool on the Content/Videos/Video page in the dashboard.
We can also provide an array of sources for our video file, from which it the player selects the most appropriate for the user's browser and player size. Each of these sources is available on the "Sources" tab of the Content/Videos/Video dashboard page. Each source also displays a poster image link that's sized similarly to the source.
Is there any way we can have the player select the appropriate poster image given the player size, similar to how it behaves with video sources? I've tried including the image fields within the sources JSON, but the player does not recognize them.