Who are UFO?
"UFO" stands for "UNIDENTIFIED Flying Object". That means we don't know what it is.
An UFO is an Unidentified Flying Object. "UFO" is a TLA ... a Three Letter Acronym ... for the phrase "Unidentified Flying Object". Once an object has been identified, it is no longer a UFO. Since those that are still listed as "UFO"s remain unidentified, it's not possible to say what they are, other than unidentified. A UFO is an abbreviation for Unidentified Flying Object.
Youtube will most definately be overflowed with UFO sighting videos and there would be several sites on the world wide web dedicated to UFO sightings which would have UFO footage in it. There are also occasionally programs on television which feature sightings of UFO and go into depth about the existence of the extraterrestrial.
That would be a most difficult thing to answer. UFO stands for Unidentified Flying Object. In order to determine what the UFO surface is like, it would have to be examined up close. If a UFO is close enough to examine the surface, then it is close enough to identify what it is and it is no longer unidentified, no longer a UFO.