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.
HEVC MKV is a digital media format that uses HEVC codec, instead of the usual H.264, which is used on typical MKV files. HEVC MKV files are encoded at lower bitrates than H.264 MKV, making them smaller by up to 50%. However, software and hardware support for HEVC MKV files is quite limited as opposed to H.264 MKV, which ranks among the most popular media formats today.
VLC Media Player
MKV File Player