Video ads will account for a quarter of overall digital ad spending this year, the market tracker predicted.

Facebook, including its Instagram messaging service, was expected to rake in nearly a quarter of all money spent on video ads with the amount tallying about $6.8 billion.

"In-feed video has been a successful ad format for both Facebook and Instagram," eMarketer principal analyst Debra Aho Williamson said in a statement.

"A newer video ad format, in-stream advertising in Facebook Watch shows, is still relatively new, but we think advertisers will increase their usage of it because it is similar to linear TV advertising."

Video ads will account for more than half the revenue at Twitter and Snapchat this year, according to eMarketer.

The market tracker said paid video ads appearing in feeds, games and apps on social platforms were included in the forecast.

Video ads are a main driver of revenue at Google-owned YouTube expected to generate $3.36 billion in a rise of 17 percent from last year.

However, eMarketer noted, YouTube tends to spend more money than its rivals acquiring online traffic.