Online media sites -- from media sites like YouTube and Hulu to social networks like Facebook, Twitter and Snapchat -- have been pushing video advertisements. But is it worth it? A new survey says ad agencies are skeptical.

About 40 percent of agencies surveyed reported that they were unsure if they actually received a good return on their investments, a new study conducted by media software company Strata and released by research firm eMarketer revealed. Additionally, about 5 percent reported they did not have a good return, and 7 percent were “really unsure.”

Not everyone was so dissatisfied or confused, however. Nearly half of the respondents reported being “fairly confident” in the results from their video ads. Yet, agencies were still unsure if their investments reached the intended audiences. Nearly 60 percent of professionals surveyed questioned if they had reached the target group. That concern comes even as some networks, such as Facebook and its photo-sharing app Instagram, boast being able to allow for sophisticated targeting.

One other concern from agencies was directed at how viewable video ads are. The eMarketer study noted data from Integral Ad Science that reports less than 40 percent of digital video ads counted as impressions -- jargon for a video that is actually viewed -- in the second quarter of 2015.

It’s worth noting that the meanings of impressions and views vary across networks. Facebook and Snapchat each having been touting billions of daily videos views -- both having reached 4 billion as of September. Yet, on Facebook, a view constitutes 3 seconds, while on Snapchat it registers after just a millisecond. These differences have been frustrating ad agencies.

“Saying we got 4 billion’s difficult to make informed choices…and it’s not really practical at scale,” Rob Norman, global chief digital officer of GroupM, a unit of global ad giant WPP, told International Business Times.

These concerns come as advertising budgets are increasingly being moved to digital platforms. Spending in digital video ads in the U.S. is expected to reach $7.77 billion in 2015, up from $5.81 billion in 2014, eMarketer predicts. The Strata poll reveals that about 56 percent of surveyed agencies were spending on digital video ads.