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Opus

 

Opus is a totally open, royalty-free, highly versatile audio codec. Opus is unmatched for interactive speech and music transmission over the Internet, but is also intended for storage and streaming applications. It is standardized by the Internet Engineering Task Force (IETF) as RFC 6716 which incorporated technology from Skype's SILK codec and Xiph.Org's CELT codec.

 

Bitrate Mode
Sets the bitrate mode. In VBR mode the bitrate may go up and down freely depending on the content to achieve more consistent quality. VBR Constrained is analogous to CBR in AAC/MP3 encoders and managed mode in vorbis coders. This delivers less consistent quality than VBR mode but consistent bitrate. With CBR, every frame will be exactly the same size, similar to how speech codecs work. This delivers lower overall quality but is useful  where bitrate changes might leak data in encrypted channels or on synchronous transports.

 

Bitrate
Sets the target bitrate in kbit/sec (6-256 per channel). In VBR mode this specifies the average rate for a large and diverse collection of audio. In VBR Constrained and CBR mode it specifies the specific output bitrate.

 

Complexity
Encoding computational complexity (0-10, default: 10). Zero gives the fastest encodes but lower quality, while 10 gives the highest quality but slower encoding.

 

Frame Size
Maximum frame size in milliseconds (2.5, 5, 10, 20, 40, 60, default: 20) Smaller framesizes achieve lower latency but less quality at a given bitrate. Sizes greater than 20ms are only interesting at fairly low bitrates.


Channels
This defines the number of audio channels contained in the output file. Setting this to Auto will attempt to create an output file with the same number of channels as the input file, if it is possible. You can also manually set it to output Stereo (2 channels) or Mono (1 channel).