It is now possible to blur out the human face before uploading video to YouTube. They have recently added this new feature which will help person uploading sensitive videos to maintain his/here anonymity.
This new blurring tool from Google will blur out all the faces from your video which means there is no option on selecting which faces you want to blur. Google also accepts that this new tool is not completely perfect which means there can be some cases in which face of a particular person in the video remains Un-blurred.
According to a reply by YouTube’s Jessica Mason to ArsTechnica she accepts the fact that it possible to unblur the faces from the video by using some tools or libraries but they have made it extremely difficult which means unblurring faces from video is not worth the effort. She also said that Unblurred version of the video is deleted from their server as soon as the editing is completed.