CUE is a text file that describes how tracks are arranged in a super-audio CD and DVDs. Typically, CUE sheets come in plain text and have a filename extension of .cue. Today, this format is prevalent in most media players and optical disc authoring apps.
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AU is an audio format standard in early web pages NEXT systems. It is also called u-law or Sparc-audio format. Typically, AU files can store audio data and annotation blocks. Initially, it was a headerless audio format, but newer versions have a header, thanks to the six unsigned 32.bit words.