The former head of the US gun lobby was tricked into rehearsing a graduation speech in front of 3000+ empty chairs. The event was fake and the chairs represented the number of high school victims of gun violence.
Whether you are in favor or against guns, the visuals of drone going over the audience with the voice in the background make an impression.
In the comments below each of the posting of the video you see the hard core pro and con camps engaging in typical uncivilized internet debating.
I think adding the sounds of gunshots and 911 calls was actually not needed at all, the effect of the video might have been better without them. It is the doubters, the ones that are sitting on the fence, who the video needs to influence. Most anti gun media has lots of noise, graphic images, and violence which might not be the right influencing strategy for the middle group. People discount it, tune out, and it sets up everyone for that heated debate that polarizes even more.