I've not tried wifi on a 747... but back when they first introduced wifi on A320's they allowed access for you to stream from sites like HBO and Netflix, but warned that streaming was not supported and was likely unreliable. But, I had some luck with it.. I suppose I was fortunate the times I tried it others were not using it. This was early on before they offered their own on board streaming options.

Now, internet streaming from all of those sites is blocked and you can't access them at all. But you should be able to stream from the on board system without any issues if you have the app.