.opus
Opus audio
A royalty-free codec standardised by the IETF in 2012 (RFC 6716), usually stored in an Ogg container. It handles both speech and music well at very low bit rates.
Voice calls, voice notes and streaming, where low delay and small size matter.
Opens in Chrome, Firefox, Edge, VLC, Audacity
About OPUS files.flac
FLAC audioFree Lossless Audio Codec
A lossless audio codec created by Josh Coalson in 2001 and now maintained by the Xiph.Org Foundation. Files are noticeably smaller than WAV yet decode to an exact copy of the original.
Archiving CDs and high-resolution music without any loss of quality.
Opens in VLC, foobar2000, Windows Media Player, Audacity
About FLAC files