Video Thumbnail is missing

[FlorianMaak]

If I visit the website via safari on ios11, there is no preview-image for the video. This should be added to trigger the users interest.

[ecklf]

iOS makes barely 1,5% of total page views atm. We can fix this if more important issues are done.

[FlorianMaak]

What about a poster-image for the video? (Think we need to ask graphics-team for it)
Would look much better, than this ugly gradient on desktop (or the black square on iOS)

[AmazingTurtle]

@FlorianMaak if you're able to, then please use ffmpeg for example to generate a thumbnail of the existing video and set is as poster.