“You want to expose it to as many people as possible, either in the moment or afterward, with context that you provide,” Mr. Pfeiffer said.
Republicans, too, have seized on live video as a tool for shaping their message. In Cleveland, the Republicans offered all of the convention speeches over the major social media networks. Donald J. Trump’s campaign organized live video from backstage, some of it delivered on Snapchat and other social networks.
“Less and less people are watching live television,” said Sam Osborne, the digital director for the Republican National Convention. Politicians who do not use live video delivered on phones and tablets, he said, “will not get your message out to the people that you need to reach.”
The idea for the Democrats’ show built off a one-hour show that they produced at the convention four years ago, hosted by the actor Kal Penn of the “Harold and Kumar” movies. Laura Olin, a Democratic digital strategist, said the video show was cutting-edge at the time. This year, instead of just one hour of programming, there will be four days of content.
“It will be at a level that we have never seen before,” Ms. Olin said.
The difference largely has to do with vast advances in technology, networks and social media apps. Facebook and Twitter have overhauled their apps to focus on live video, and other companies that focus on using video, like Snapchat, have emerged in recent years.
Facebook introduced Facebook Live this year, and has partnered with campaigns and news media organizations to produce content. For the conventions, the company is using the live-streams of news outlets and the parties held during the events as a way of bringing the programming of the conventions to users’ screens.
Twitter is planning a similar effort with live broadcasting. In addition to its Periscope app, the company has introduced a new live-streaming video platform that teams up with broadcasters to provide high-definition video for Twitter users on the platform’s app or website. For the convention broadcasts, Twitter became partners with CBS News. Alongside the stream, Twitter users will be able to send out posts and read their own feeds.
“It’s a recognition that often people are tweeting as they watch something on TV, so the hope is this is one experience,” said Nick Pacilio, a Twitter spokesman.
The presidential campaigns have fully embraced digital media as a central part of their messaging and organizing strategy. In June, at a senior-level planning meeting at Mrs. Clinton’s headquarters in Brooklyn, members of the digital team almost jokingly proposed an online contest to select a constituent to have a role at the Democratic convention. The campaign’s top strategists immediately agreed.
The campaign has also invited celebrity supporters to use social media as an organizing tool in a nationwide effort to register three million voters. And Mr. Goff said the campaign was using its digital media presence to bolster its collection of email addresses and other valuable information about voters.
Smartphones, and the extensive use of social media by campaigns to communicate directly with voters, often provide a view into places that previously would have gone unseen because of limited access of the news media, especially at conventions. Instagram’s Backstage Portrait Studio at both conventions captures the final moments before a speaker, or eventually the candidate, takes the stage.
And Snapchat has proved unusually adept at gaining behind-the-scenes access at closed-door events like fund-raisers. Delegates, campaign aides and convention officials used the platform at the Republican convention, and the company expects the same among Democrats in Philadelphia.
For those who attend the conventions in person, the most prominent social media platforms have been at least as visible as the broadcast television and cable networks.
The bright royal blue hue of Facebook dominated large spaces in the convention hall and news media filing centers, providing coffee, snacks and real-time data for journalists and, for delegates and convention attendees, hands-on trials of the company’s virtual reality product Oculus. Facebook also built a studio adjacent to the arena to allow its news partners, including The New York Times, to produce live segments.
Twitter has booths scattered around the convention site, but is also focusing offsite. As it did last week in Cleveland, the company is renting out restaurants and event spaces to host meetings and panel discussions on the platform’s role in the election, with topics like #BlackTwitter and women in politics.
But for the Clinton campaign, the goal of these efforts is to reach an audience well beyond Philadelphia.
A campaign spokesman said that what he called “gavel-to-gavel coverage” of the convention would be distributed to viewers on Apple TV, Amazon Fire and Roku, in addition to Facebook, Twitter and Snapchat.
Mr. Goff said that Mrs. Clinton’s strategists were not ignoring the traditional broadcast and cable networks. But he noted that 2014 was the first year that Americans, in aggregate, had spent more time in front of their smartphone screens than they did in front of their television screens.
“TV is still really important,” Mr. Goff said. “But things are changing really quickly.”