Please use closed captioning, even if it's lousy auto-captioning
Closed captioning on videos would be great, please. I know that the sources don't always provide the captioning, but when they're clips from TV news, they really should. IF GMA and local news channels want their clips to have global exposure on Yahoo!, then it should be part of their deal with you that they include the captions they were required to provide when they were on the air.
There is software in existence now, too, that will do an auto-caption; it's generally a pretty poor caption compared to having a trained person do it, but it's better than nothing at all.
I'm certain there are plenty of deaf or hearing impaired users of Yahoo!, as well as users in public spaces like libraries, who cannot take advantage of audio. Captioning of videos would be a tremendously helpful service.