Hulu and YouTube both launched livestreaming services last year to take on big cable companies with packages of online TV channels. It's still early, but they're making some progress, according to numbers revealed to CNBC.

Hulu's live offering has about 450,000 paying subscribers, not including recent promotional customers, according to people familiar with the matter. YouTube TV has just more than 300,000, said the sources, who asked not to be named because the numbers are private.

Neither Hulu nor Google, which owns YouTube, have formally announced subscriber numbers, and representatives for both companies declined to comment for this story.

Over-the-top providers of live content are gauging how many American households have an appetite for live online video as an alternative to traditional cable packages. YouTube TV costs $35 a month, and Hulu with Live TV costs $39.99 per month, with both offering viewers a combination of live sports, news and events from a host of networks. Hulu's product also includes its standard offerings of video on demand.

While they have a certain appeal to cord cutters, Hulu and YouTube may struggle to substantially grow their customer base because canceling is so easy and the value proposition compared with video on demand isn't very good, said Rich Greenfield, an analyst at BTIG.

"If you don't care about live sports, the original Hulu product is awesome," Greenfield said. "You can get all of the programming you want for more than $30 less. And YouTube is free. It actually shows you how poor the value proportion is for live TV."

Hulu, which competes with Netflix and Amazon Prime Video, costs $8 a month for an online library of TV shows and movies. Hulu announced earlier this month that it has more than 17 million paying customers spread across both its on-demand and live TV services.