This video shows early footage from Black Mesa: Source a mod that's been in development for a long time now.
This footage is from Surface Tension chapter on the mod. I know it's an awful quality, but it's been leaked this way. The guys at LambdaGeneration have found this footage and shared it with us. The footage also comes from a fairly old and now outdated mod development build. This means, this isn't what you'll find in the mod when it's released. The music on the background was added because the video had no sound at all.
Thanks to the guys at LambdaGen, I take no credit in the finding of this video, thats why I didn't edit the video so it looked like mine. More info at: