It’s that time of year again, when the TV networks talk about how great their upcoming fall shows will be — and everyone else talks about whether they will survive the relentless onslaught of OTT, cord-cutting and myriad other challenges.Social media is one of those challenges. Companies like Facebook have never been shy about touting themselves as excellent companions to TV. They routinely conduct research studies that show lifts in seemingly every metric imaginable, as long as ad buyers use TV and social together.But this year, eMarketer believes the conversation about social and TV will change. For buyers who want the best way to reach their audience, the growing video businesses of Facebook, Instagram, Twitter and Snapchat now present a viable alternative to TV.Related StoriesUpfront Uproar: Inside the Fall’s 5 Toughest TV Time SlotsFunny or Die Takes Down the Upfronts’ ‘All New’ LineupsBefore I go on, it’s important to say this: It’s not as if vast sums of money will shift from TV to social this year — or even next year. This year, $70.6 billion will be spent on TV advertising in the US, according to eMarketer. Investment bank Cowen and Co. predicts Facebook’s video ad revenue will be roughly $2 billion worldwide this year. So we’re talking about a relative trickle right now. But the trickle can very easily become a strong flow.Several factors lead me to this conclusion:The broad availability of video ads on social platforms. In the two short years since Facebook rolled out premium in-feed video ads, other social platforms have followed suit with their own video ad products. And the inventory keeps expanding; this week, Facebook said it would start selling in-feed and in-article video ads on properties that are part of its third-party ad network.The TV-like reach and appealing demographics that some platforms offer. Companies like Snapchat and Facebook routinely compare their audience to TV. Snapchat, for example, has touted the fact that up to eight times as many 13- to 34-year-olds in the U.S. view Live Stories versus TV for similar events. And Facebook COO Sheryl Sandberg once famously compared Facebook’s reach to the Super Bowl.