What are the most popular albums in any given week?

For Billboard, the 125-year-old music trade publication, that was once a simple question. Its charts were based on the number of CDs, vinyl LPs or tapes that fans bought at stores.

But compiling its weekly charts has only gotten more complicated with the rise of streaming formats — some free, some paid — and as record companies have found ways to game the system by including free downloads of new albums with the sale of merchandise or concert tickets.

Now, in the latest change to its chart rules, Billboard has tackled one of the industry’s most contentious questions: the role of YouTube, which dominates music consumption online but has frequently been vilified by record companies — and even many of the artists who post videos there — for low royalty payments.

Starting Jan. 3, Billboard will count the popularity of official music videos on YouTube, as well as those on Apple Music, Spotify, Tidal and Vevo, in the magazine’s flagship album chart, the Billboard 200. (YouTube plays have been part of Billboard’s singles ranking, the Hot 100, since 2013.) User-generated content — like memes or cover versions — will not count.