Windows Media Audio (WMA) was introduced by Microsoft in 1999 as a competitor to MP3, and while it was slow to catch on at first, its popularity has increased in recent years. Several online music stores--including Napster--use WMA (with Digital Rights Management) as the basis of their service, and a growing number of portable digital players support the format. WMA files are usually wrapped in an Advanced Systems Format (ASF) file, a fully documented format that provides streaming capability.
Microsoft's Windows Media offerings include an encoder (Windows Media Encoder), various software development kits, and a player (Windows Media Player). There are both lossy and lossless codecs available for WMA.