iFrames must be either 600px away from the top or not within the first 75% of the viewport when scrolled to the top – whichever is smaller. This example might not work depending on your screen width. In this case it will only show an loading indicator.
The 600px away from the top constraint can be avoided بواسطة adding a placeholder image.
If the video is 600px below the top, no placeholder image is required.