Container Format
A WMA file is in most circumstances contained in the Advanced Systems Format (ASF), a proprietary Microsoft container format for digital audio or digital video. The ASF container format specifies how metadata about the file is to be encoded, similar to the ID3 tags used by MP3 files. Metadata may include song name, track number, artist name, and also audio normalization values. This container can optionally support digital rights management (DRM) using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function. See Windows Media DRM for further information.
Since 2008 Microsoft has also been using WMA Professional in its Protected Interoperable File Format (PIFF) based on the ISO Base Media File Format and most commonly used for Smooth Streaming, a form of adaptive bit rate streaming over HTTP. Related industry standards such as DECE UltraViolet and MPEG-DASH have not standardized WMA as a supported audio codec, deciding in favor of the more industry-prevalent MPEG and Dolby audio codecs.
Read more about this topic: Windows Media Audio
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