(The film itself starts about 2 minutes into the video.)
Slashflim: Lucas commissioned the original Black Angel short film to play as a companion piece with Star Wars: The Empire Strikes Back in some markets. It was well received and became a major influence on fantasy films that followed. But shortly after its premiere, all copies of the film were lost.
… Or so everyone believed until 2011, when a Universal Studios archivist came across a negative. An effort to restore the film got underway, and the film “re-premiered” at the Mill Valley Film Festival in 2013. Black Angel got a digital re-release in 2014, and as of last month was available to stream in its entirety on YouTube.