A metallic wafer of video and sound, the A815 is Sony’s first Walkman to let you use Windows Media Player instead of the much-reviled SonicStage, and proper music formats instead of the under-supported ATRAC.
Aided by high-quality headphones, sound quality is outstanding, while the 26-hours batery life is relatively sprightly. As a bonus, movies look magnificent on the bright, two-inch screen.

The A815 is a real winner. Now it’s compatible with the rest of us, Sony’s Walkman can rule the world again.

Capacity : 2GB
File Formats : MP3, WMA, AAC, MP4
Screen : 2 inches
Size : 4.5 x 8.8 x 1.0 cm

Source: http://hardwaretechreview.com/sony-nwz-a815-review