Any steganography solution on the market today that is worth its salt would actually be robust against this. The amount of different sources you would have to combine to protect against this is higher than you'd realistically be able to find.

Disclaimer: I used to work at one of the leading companies in this field.

That's very interesting. I always assumed averaging (maybe with varying weights across frames and time), or applying a few rounds of other steganography, would degrade the encoded message into noise.

Could you link to some papers? If you try to encode lots and lots of messages with different keys into the video, does it ruin the quality before ruining previous messages?

I'm not sure in how much details I can go since a lot of this is behind patents and NDAs and whatnot, but just googling for "video watermarking" should already yield quite a few interesting details for you.

the algorithm could tell exactly which sources are used in the final video?

impressive!

Are you being sardonic? There are extremely obvious ways to do this particularly since they've got both space, color, sound and particularly time to play with. Unmixing signals isn't rocket science, especially if you've provided the signals that are getting mixed.

it's amusing to me, how much effort people are willing to put in to get free entertainment.

Even better? Those of us who do it all after paying for the service.

Sometimes, it's not about the money.