The person who took the video and posted it to YouTube described the experience as follows:
"This is a Yellow-bellied Puffing Snake (Pseustes sulphureus). We first detected this guy because two Guianan Toucanets were making a ton of raucous near the bottom of a tree. A closer inspection revealed a snake which we estimated to be over 3m (10ft) long, the largest I have ever seen in the wild. Upon approach, the snake did not attempt a retreat as I'm used to, but charged instead and the resulting brawl in the thick understory must have been a sight to behold. This video is the aftermath, where this bad-tempered serpent is much calmer - believe it. What a badass snake."
The footage was taken in central Brazil.