Apple continued to dominate the US digital music player market in the second quarter with a 75.6 percent market share, according to the NPD Group.

"Apple has done a great job of focusing consumers' attention on digital music in their products through millions of dollars in advertising," said Ross Rubin, analyst at the NPD Group.

But it's hard to tell if Apple will be able to maintain its sizable lead as mobile phone companies continue to put out handsets with built-in music players. A number of analysts have warned that the digital music player market could go the way of the PDA, which saw growth drop off once mobile phone companies introduced smartphones – handsets with PDA functionality.

Rubin says companies focused on standalone digital music players should remain competitive against the mobile phone industry because their devices have greater capacity, better user interfaces, better integration with online music services and stronger DRM (digital rights management) support.

US mobile phone service providers have also hindered the popularity of using mobile phones as music players because they have been charging more for purchasing songs online than their rivals in the standalone music player business, Rubin said. Carriers have also in some cases been reluctant to enable music file exchange with computers using memory cards or Bluetooth, instead preferring that consumers rely on their networks for purchases, he added.

But he noted that mobile phone companies are getting better at the music business, especially in recent handset models.

SanDisk followed Apple in the Q2 ranking with a 9.7 percent market share, according to the NPD Group, while Creative took third place with 4.3 percent of the US digital music player market.

Samsung sat in fourth place with 2.5 percent, while Sony holds 1.9 percent of the market.