opus

Documentation

Overview

Package opus wraps the Opus codec for jargo's audio path: it decodes Opus packets to PCM on the way in and encodes PCM to Opus packets on the way out.

The codec runs at 48 kHz — the rate WebRTC negotiates for Opus — so audio crosses the transport without resampling. Encoding produces 20 ms frames, the standard WebRTC packetization.

The decoder is pure Go. The Encoder has two builds selected by the `libopus` build tag (see encoder_pion.go / encoder_libopus.go): the default is the pure-Go encoder; `-tags libopus` links the C library for higher speech quality. Both expose the same NewEncoder/Encode API.

Index

• Constants
• func FrameBytes(channels int) int
• type Decoder
  • func NewDecoder(channels int) (*Decoder, error)
  • func (d *Decoder) Decode(packet []byte) ([]byte, error)
• type Encoder
  • func NewEncoder(channels, bitrate int) (*Encoder, error)
  • func (e *Encoder) Encode(pcm []byte) ([]byte, error)

Constants

const (
	// SampleRate is the codec sample rate in Hz. Opus runs at 48 kHz.
	SampleRate = 48000
	// FrameDuration is the duration of one encoded packet.
	FrameDuration = 20 * time.Millisecond
	// FrameSamples is the number of samples per channel in one 20 ms frame.
	FrameSamples = SampleRate / 1000 * 20 // 960

)

Functions

func FrameBytes

func FrameBytes(channels int) int

FrameBytes is the size in bytes of one 20 ms S16LE frame for channels.

Types

type Decoder

type Decoder struct {
	// contains filtered or unexported fields
}

Decoder decodes Opus packets into signed 16-bit little-endian PCM.

func NewDecoder

func NewDecoder(channels int) (*Decoder, error)

NewDecoder builds a Decoder that outputs channels-channel 48 kHz PCM. It decodes all Opus modes (SILK, CELT and hybrid).

func (*Decoder) Decode

func (d *Decoder) Decode(packet []byte) ([]byte, error)

Decode decodes one Opus packet into interleaved S16LE PCM bytes.

type Encoder

type Encoder struct {
	// contains filtered or unexported fields
}

Encoder encodes 48 kHz S16LE PCM into Opus packets using the pure-Go pion encoder. This is the default build. The encoder is currently CELT-only, which is weaker on speech than libopus; build with `-tags libopus` for the C library instead (see encoder_libopus.go).

func NewEncoder

func NewEncoder(channels, bitrate int) (*Encoder, error)

NewEncoder builds an Encoder for channels-channel 48 kHz audio at the given bitrate in bits per second; pass 0 for the codec default.

func (*Encoder) Encode

func (e *Encoder) Encode(pcm []byte) ([]byte, error)

Encode encodes exactly one 20 ms frame of interleaved S16LE PCM — that is FrameBytes(channels) bytes — into a single Opus packet.