Entertainment companies have yet another social-marketing tool to play with: Yahoo’s Tumblr micro-blogging site has launched autoplay video ads, with initial advertisers including Universal, CW and Hulu.

The video ads on Tumblr will show up in users’ feeds, muted by default and presented in a continuous loop — like Facebook’s autoplay ads. On Tumblr’s Android and iOS apps, the videos ads will autoplay only when a user is on a Wi-Fi connection.

CW’s ads will promote two new fall shows — “The Flash” and “Jane the Virgin” — and Universal will use the video ads to pitch Nov. 14 theatrical release “Dumb and Dumber To” starring Jim Carrey and Jeff Daniels (pictured, above). Hulu’s Tumblr ads will be part of the Internet TV site’s “For the Love of TV” campaign.

For Yahoo, the new video ads come as the company is under pressure to show investors that the $1.1 billion Tumblr deal can produce a significant revenue stream. CEO Marissa Mayer, on the company’s earnings call last week, said Yahoo expects Tumblr to top $100 million in advertising revenue in 2015.

There’s certainly an audience on Tumblr — the site claims to have 420 million unique users, with time spent on the site growing to an average of 28 minutes per session in Q3 2014, up from 22 minutes when Yahoo bought the site 15 months ago. But it remains to be seen how receptive Tumblr’s user base will be to the appearance of auto-playing video ads on the site.

Tumblr is launching the pilot test of the video ads starting Tuesday with the initial beta partners, which also include Lexus, JCPenney and Unilever’s Axe. The site expects sponsored video posts to be widely available to all marketers in mid-November. Tumblr isn’t disclosing pricing, but is charging on a cost-per-view model for video ads (and only after the ad has played in-view for at least 2 seconds).

The autoplay ads are part of Tumblr’s enhanced native video player, launched last week. The player features a pop-out video player and a “floating” video window that docks to the right allowing users to keep scrolling through the dashboard while continuing to watch the video.

Tumblr claims video posts have been growing twice as fast as photo posts, but it has declined to disclose actual numbers of views in each category.

Since Yahoo’s acquisition, Tumblr has made an effort to reach out to media and entertainment marketers to use the site and buy ads. To date, Tumblr has executed promotional campaigns with partners including NBC’s “The Voice,” Lionsgate’s “Hunger Games,” AMC’s “Halt and Catch Fire” and Viacom tied to TV programming for networks including MTV, Nickelodeon and Comedy Central.