This is a very common problem and normally caused by bandwidth. Either your connection is slow at the moment or the host website (YouTube) is busy and running slow.
There is a very simple trick to overcome this:
- Click the video Play button and once the video begins to play
- Click on the Pause button.
The video will continue to upload to your computer, though it is in a paused state. You can monitor this by watching the Progress Bar.
- After the Progress is completely full or complete, click the Play button again and watch the video uninterrupted.