I'm seeing some assertions about this on blogs and in YouTube videos, and it's wrong if not unfair and deceptive. I don't have my own video, because I mishandled the button on my camera, but I was right behind the Tea Party crowd amid anti-Tea Party protesters who were making a lot of noise trying to drown out whatever was coming from the podium. They were, in fact, succeeding in their purpose so well that they could not hear when the national anthem began.
I started walking forward and it took a while for me to recognize the anthem. My observation was that those who could hear it were not booing. The "rockets red glare" line seemed louder, and there was a noticeable hushing that extended back into the anti-Tea Party areas of the crowd.
Meade and I have observed some of the most raucous rallies at the Capitol over the last 2 months, and the national anthem was sung many times, by the protesters themselves, and we witnessed respect for the anthem. In fact, you could go into the rotunda and start singing the anthem and people would go silent and even sing along with real feeling. They might have resented having to switch to solemnity when they were into raucousness, but they knew very well that they had to at least look like they respected the anthem.
Outdoors, yesterday, the acoustics were distorted, the anthem began unexpectedly, and the noisemakers were into their thing, drowning out the tea partiers. You cannot infer disrespect for the national anthem. But if you want to get back at people who are trying to drown you out, it's a good trick to start singing the anthem, while video-recording.... though maybe that's not properly respectful of the anthem.