That's the kind of situation that watermarking handles well. With no time to remove the watermark, it would be straightforward for the stream source to find the offending stream consumer and shut down their stream.
But the stream source would then have to be very active in hunting for unauthorised mirrors, because there would be nothing to find after the event has ended.
If the piracy is happening on a large scale, it should be easy to find the unauthorized stream. If the piracy is happening on a small scale, then it's not a big problem for the stream source.
What if it's happening on a small scale many times over? Thousands of links, posted to forums in all kinds of languages.
And we're both assuming that the people running those mirrors won't work out a way to disable the watermarks in real time. I've not read up on digital watermarking technology, but it's hard to imagine that it's bulletproof.
Fair point. I think detecting and booting some fraction of those streams would have a deterrent effect on the rest, but who knows for sure unless it gets tried?
And yes, I'm assuming that robust-enough watermarking methodology is possible. I don't think it has to be bulletproof, I just think it has to be good enough to enable cancelling enough stream consumer accounts to deter casual mirror-ers. DRM isn't bulletproof either; watermarking is preferable for users because it doesn't require that the stream producer take control over your machine.