OPUS is a audio codec mainly used for voice transmission over the internet, including applications of Voice over IP (VoIP), audio streams, or video chats. Audio music file with .OPUS file extension also use this encoding technology, but are rather uncommon. Some audio players may not support such files.
OPUS is a lossy audio compression format. It is designed as an efficient human speech and music audio encoding scheme within given bandwith limitations.
OPUS codec has been developed as a result of combining two encoding algorithms:
encoding algorithm used by Microsoft Skype and licensed audio codec, currently available as an open-source technology for non-commercial use only
codec used by TeamSpeak3 and some computer games that offer voice-chat feature
Combining these two technologies and improving on them allowed to create a codec that offers low latency (in the range of milliseconds) and superior compression ratio at the time of it release. The biggest advantage of Opus is the ability to dynamically change compression ration to achieve optimal balance between audio quality and data loss/latency. Opus offers 16-bit depth at up to 48 kHz sampling rate, well within accepted standard values for human hearing range.