OPUS is an audio file that is encoded using the Ogg Opus format (lossy coding). It was created for online audio streaming, that is, in order to transmit sound through a global network. The format is being developed by the Internet Engineering Task Force (IETF) and Xiph.Org communities. Applies SILK codecs when used in Skype and CELT (from Xiph.Org), provides support for variable bitrate. Most often, the OPUS codec is used for video conferencing, game chats, VoIP telephony. OPUS is a free audio codec that has international standard status (IETF RFC 6716). Its main advantages are a low coding delay (from 2.5 to 60 ms) and its significant speed, an increased degree of compression of audio data with high-quality sound, as well as support for multi-channel audio (within 255 channels). In 2011, J. Skeglund of Google conducted two series of tests, during which OPUS coding and decoding were compared, taking into account the assessments of experts and ordinary listeners. Studies have shown that OPUS provides stereo music with the same quality as MP3 and better quality than G.719 64 kbps. OPUS offers great streaming capabilities with dynamic tweaking and very low latency. This is always high sound quality and excellent data compression. Full support for OPUS is provided by Mozilla applications. He is the key Skype audio codec.
M4V is a video file format that has been downloaded from the Apple iTunes store. The format contains TV shows, videos, films, music. It looks like a .MP4 file, but it sometimes has copy protection when Apple's FairPlay DRM is used (technical copyright protection). The M4V format, i.e., MPEG-4 iTunes Video File, was developed by Apple. MP4 is a container format. Like the same formats as MOV, AVI, MKV, it provides the ability to combine a variety of multimedia streams into one file. Mostly it is audio and video. In order to play the protected M4V file, the computer must be authorized using the iTunes account from which the videos were purchased. In this case, it can be used in order to buy video. Unprotected M4V files can be played by other video players if the extension is changed from .M4v to .Mp4. Files with the M4V extension contain both sound and video data. You can convert M4V files to MP4 format. In this case, it will be possible to play them on other computers, since the M4V files are protected by DRM. MP4 files, compared to the M4V format, do not allow you to specify partition information.