Any delay in starting a clip probably indicates that the YouTube website is very busy, although not all videos will have YouTube as their source.
If there are problems playing a clip (e.g., ending part way through), click on the YouTube logo (bottom right corner) to play it at the YouTube website. The YouTube site will open in a new window, leaving this window intact.
If you don’t already have Adobe® Shockwave Player installed, click on the following link to download and install it.