The feature — called See It — will initially be turned on only for Twitter posts published by Comcast-owned channels, like NBC, about their shows, like “The Voice.” But the companies said they were talking with other distributors and channel owners about extending the feature to other shows. Eventually Comcast wants See It to show up on other Web sites and apps as well, so that online conversation and news coverage about TV series and movies can directly lead users to those series and movies.

The technology will test the interconnectedness of television and the social Web, two media platforms that enhance each other while also competing for advertising dollars and attention. It was announced as part of a broader partnership between Twitter and Comcast, the nation’s largest cable television provider. It comes as the privately held Twitter prepares to sell stock to the public.

For Twitter, the feature is another opportunity to promote itself as a destination for television conversation and as a friend to the networks.

As part of the announcement on Wednesday, NBCUniversal, the umbrella company that includes channels like NBC, the NBC Sports Network, USA, and E!, said it would join Twitter’s Amplify advertising program, which attaches ads to short video clips distributed through the social networking service. ESPN, Fox and CBS are among other participants in Amplify.

But what attracted attention in the industry on Wednesday was See It, which is to start appearing on Twitter in November. In a statement, the Comcast chief executive, Brian L. Roberts, called it a “simple yet powerful feature that creates an instant online remote control.”

The feature overlays parts of a cable television subscription onto Twitter: when NBC publishes a post about “The Voice,” for instance, a See It button will appear at the bottom of the post, encouraging the user to take some sort of action. Users who click the button will be asked to log in with their cable user name and password, the same way they have to log in to watch on-demand programming online.

In the beginning, Comcast customers who log in will be able to, depending on the circumstances, start watching “The Voice” live on their big-screen TV or mobile device; start watching an on-demand version of the show; or set their digital video recorder to record the show though the See It feature. Twitter users without a Comcast user name and password will be directed to NBC’s Web site or app to watch the videos there. “Our expectation is that we’re going to have other multichannel distributors and other programmers as part of this platform pretty quickly,” said Samuel Schwartz, the chief business development officer for Comcast Cable.

Persuading Comcast’s and Twitter’s rivals to participate may prove difficult, though. When asked whether the See It feature could appear on Facebook, Mr. Schwartz didn’t answer directly, but said, “Ultimately, it could be on every part of the Web and every app.”