Comic-Con doesn't live-stream its panels, mainly to give the people who spend lots of money and travel from far and wide the feeling that they are getting something special for being there. But most of the clips screened at Comic-Con panels quickly find their way online, and more and more frequently through official channels, as has happened today with two different Steven Moffat shows.
For instance, here's a scene from the “Sherlock” Christmas special that transports the characters, still played by Benedict Cumberbatch, Martin Freeman, et al, back to their literary Victorian roots:
And here's the new “Doctor Who” trailer, which includes Maisie Williams and a bunch of other footage that Donna Dickens breaks down in greater detail in her live-blog of that show's Comic-Con panel: