IE Market Research's Global Digital Music Forecast for online, mobile, and subscription channels predicts that retail revenues will increase to $32.5 billion by the end of 2014.The forecast sees most of the growth coming via music subscriptions both online and mobile.

Other key findings:

• There are now 832 million paid users of digital music worldwide and that number is expected to almost double to 1.555 billion in 2014.
• While the number of music users downloading their music through their mobile handsets will increase from 507 million in 2009 to over 1 billion in 2013, the greatest growth in the global digital music industry will happen through subscriptions to both online and mobile music channels
• Digital Music revenues at record companies will increse from a current $4.82 billions to $21.3 billion at the end of 2014   

North America

• There are now 105.4 million paid users of digital music in North America and that number is expected to grow to 227.2 million in 2014
• Online music download users in North America will increase dramatically from 50.4 million in 2009 to 135.0 million in 2014
• Digital music retail revenues in North America to reach $11.86 billion in 2014

For more detail and other territories, you can read the execitive summary here.