To what extent are the circulating video clips on the internet that show angels on the surface of the Holy Kaaba authentic?

We cannot ascertain the authenticity of what a person sees in a video. However, the Sacred House (Kaaba) is a focal point of mercies and blessings, a place where angels descend due to the abundance of worship performed there. There are Hadith (definition) that indicate the descent of tranquility (Sakina) and angels when the Quran is recited and Allah is remembered, such as the Hadith narrated by Usaid ibn Hudair, Al-Bara' ibn Azib, and Abu Hurairah. Seeing angels is possible both in wakefulness and in dreams.