I am using the iOS YouTube Player helper (https://developers.google.com/youtube/v3/guides/ios_youtube_helper) and it works just fine but the preview image is not the size of
A bit late to the party, but since none of the other solutions worked for me, I solved it by constraining the webView / YTPlayerView to a 16:9 aspect ratio as that is the standard aspect ratio for YouTube videos according to this:
https://support.google.com/youtube/answer/6375112?co=GENIE.Platform%3DDesktop&hl=en
With your webView/playerView the same aspect ratio as the video, the preview image will display properly.