Nielsen just removed any doubt that streaming music is here to stay. The research group's end-of-year music report reveals that the number of on-demand US streams nearly doubled year-over-year in 2015, to 317.2 billion streams. Downloads unsurprisingly took a hit, with individual song sales diving 12.5 percent and whole albums dropping 2.9 percent. However, the sheer volume of streams appears to at least partly make up for the shortfall -- Billboard notes that the revenue is equivalent to 211.5 million purchased albums. While artists aren't necessarily getting all that extra money, it's a positive sign.