Well, its a bit late for answer, but someone might stumble on this post and might get an insight.
I was facing the same issue and 1st option below solved my problem.
After a lot of search regarding the similar issue, I came across two things.
1) Check if your YoutubePlayerView (in activity XML) has padding option. Remove the padding if its there.
2) As per youtube Api documentation, the minimum size specified is 200 x 110 dp for YoutubePlayerView. Make suitable changes in size if that is the case.
Hope it helps somebody.