The digital music industry is set to double from $7.4 billion to $20.1 billion in 2015, according to a new study. That's a compound annual growth rate of 22.1% over the period. Subscriptions will be the fastest growing segment, growing at a compound annual rate of 60.8% to 2015.

In terms of digital music market value, the US, Japan, UK, France and Germany are the key digital music markets, together accounting for 79.5% of the global market in 2010. India, China, and Mexico are the upcoming digital music markets, which present strong growth potential, according to the report.

On fact driving the growth, according to the study, it that globally, ISPs are entering the battle against music piracy, primarily driven by the collective efforts of music companies and local governments. In 2010, France, Ireland and South Korea took steps to curtail music piracy, while others including the UK, New Zealand and Malaysia are aiming to do so in 2011.