The ads would probably first appear in Facebook videos by professional publishers, said one analyst.
To date, the social network has resisted allowing "pre-roll" ads that play before a video starts.
Publishers would receive 55% of revenue from mid-roll ad sales, according to tech site Recode.
Facebook declined to comment.
"Advertisers are super keen on video advertising," said Eleni Marouli, at analyst company IHS Markit.
