"We wanted to find that new and expressive way of communicating," Yahoo senior vice president Adam Cahan said at a New York media event for the app called Livetext.
Cahan said the Yahoo team chose to focus on video without audio to encourage people to use the app in a variety of situations.
"We wanted to make sure there is no inhibition of answering or connecting," he said.
With audio, he said, Yahoo found that in many situations, people "are not willing to engage."
At the event, product manager Arjun Sethi demonstrated "conversations" over smartphone connections that showed live facial expressions accompanied by text and emoticons.
"We see video as a way to make your conversations more authentic, and we see text as a way to connect that's quick and non-intrusive," Sethi said.
It has already been tested and is available in Hong Kong, Taiwan and Ireland.
The move comes with Yahoo aiming to refocus its business on mobile and video after losing leadership in Web search.
"Every platform shift leads to new forms of communication, driven by our desire to connect and interact in richer ways," Cahan said in a statement
"We wanted to create a new way to communicate, blending the simplicity of texting with the emotion and immediacy of live video, to make your experience spontaneous and real."
Sethi came to Yahoo from the mobile messaging application MessageMe, acquired by Yahoo last year.