Just google it tbh
or use a bit of common sense, im tired of the dumbassery of people. But its been common knowledge for a while. Because you asked the question, im pretty sure your own research skills are negligible so let me point out this, alot of mainstream media uses only data gleamed from stores (which is that cd hardcopy data is down about 12% this year. Ignoring the nearly 30% increase in digital sales)
You definitely can't make a claim like that and then say it's "common knowledge". In fact this is probably knowledge that no one can claim to hold.