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.
AVI (Audio Video Interleave) is a digital multimedia container format developed by Microsoft in 1992 for its Video for Windows project. This file format saves both video and audio data in its container that supports synchronous audio-with-video playback. And like DVD format, AVI allows multiple audio and video streaming as well.
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