"Can't be blocked" is impossible. Even if you don't know the location of the source (say, they're using a censorship-resistant system such as a Tor hidden service), you can still perform a denial-of-service attack, though doing so would have substantial collateral damage (a successful DoS on a Tor hidden service will likely render the entire Tor network unusable).
If you can find the source of the stream, there are many ways of blocking it, of varying degrees of legality, ranging from sending a takedown notice to the relevant ISP, to BGP hijacking.
"Can't be traced" is a different matter. Censorship-resistant networks such as Tor or Freenet are designed to be difficult to trace: finding a Tor hidden service might require the cooperation of eight different countries' police forces (six for the Tor nodes passing data along, plus the investigating country and the one the server is in). Freenet is even harder: unless you're watching as someone uploads a file to the network, it's impossible to tell the original source of that file.
In the scenario described in the question, the use of Tor is unlikely: Tor's latency is too high and the bandwidth too uncertain for streaming video. Additionally, there's no way to have "partial" knowledge of someone's location: it's either all or nothing. Freenet can't have been used, since it's essentially a distributed file store rather than a network of servers; streaming video over Freenet is impossible.