The captcha seems to work fine from here.

Have you tried guessing the captcha before viewing the video? If that is the case, then you have been blocked out and need to wait a few minutes for it to work again.

Entering the captcha text before viewing the video is not possible, and will result in you being blacklisted for a moment by the captcha provider. All you can do is wait for it to work again.

EDIT: Let me know if this is not the case