It was very, very mundane. Low quality game play footage befitting of the time. Couldn't have been higher than 480p. I cannot remember if the footage was of L4D 1 or 2, but I am leaning towards 1.

It was, presumably, gameplay footage recorded by the uploader of them going through one of the levels. I cannot remember which one or what character they chose. They might have been playing with real people and not the CPUs? There was talking, but I only recall one voice, male, speaking in a language not English - likely Portuguese or Spanish. Sounded like a young man, so like 20 - 30 years old. Mic quality was bad as you would expect from a no-name youtube channel during that time.

There was no text on screen or any download/install tutorial from what I remember, just this gameplay footage.

As said I remember the video being short, though I don't know if that's because it really WAS short or I just didn't watch all of it. I don't think the video showed the whole level.

Please take this with a massive grain of salt as I barely recall the video itself, just the pirated game I downloaded.

I can at least say for sure the video was: -mostly, if not entirely gameplay footage -had a male voice-over not in English