83 lines
2.3 KiB
Go
83 lines
2.3 KiB
Go
package nativeaudio
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import (
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"encoding/binary"
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"errors"
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gopus "github.com/thesyncim/gopus"
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)
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const (
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SampleRate = 48_000
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Channels = 2
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FrameSamples = 960
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FrameBytes = FrameSamples * Channels * 2
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MaxPacketBytes = 4_000
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DefaultBitrate = 128_000
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defaultComplexity = 5
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)
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// Encoder adapts the capture process's fixed 48 kHz PCM frames to WebRTC
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// Opus packets. The buffers are owned by the encoder and reused after each
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// Encode call; the returned packet must be consumed before the next call.
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type Encoder struct {
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codec *gopus.Encoder
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pcm [FrameSamples * Channels]int16
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packet [MaxPacketBytes]byte
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}
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func (encoder *Encoder) Bitrate() int { return encoder.codec.Bitrate() }
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func (encoder *Encoder) SetBitrate(bitrate int) error {
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if encoder == nil || encoder.codec == nil || bitrate < 6_000 || bitrate > 510_000 {
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return errors.New("native audio bitrate is outside the Opus range")
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}
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return encoder.codec.SetBitrate(bitrate)
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}
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func NewEncoder(bitrate int) (*Encoder, error) {
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if bitrate < 6_000 || bitrate > 510_000 {
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return nil, errors.New("native audio bitrate is outside the Opus range")
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}
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codec, err := gopus.NewEncoder(gopus.EncoderConfig{
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SampleRate: SampleRate,
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Channels: Channels,
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Application: gopus.ApplicationAudio,
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})
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if err != nil {
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return nil, err
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}
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if err = codec.SetBitrate(bitrate); err != nil {
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return nil, err
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}
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if err = codec.SetComplexity(defaultComplexity); err != nil {
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return nil, err
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}
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codec.SetDTX(false)
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if err = codec.SetInBandFEC(gopus.InBandFECDisabled); err != nil {
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return nil, err
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}
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return &Encoder{codec: codec}, nil
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}
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// Encode accepts one interleaved little-endian PCM16 frame and returns an
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// Opus packet backed by the encoder's reusable output buffer.
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func (encoder *Encoder) Encode(pcm []byte) ([]byte, error) {
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if encoder == nil || encoder.codec == nil || len(pcm) != FrameBytes {
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return nil, errors.New("native audio PCM frame is invalid")
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}
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for index := range encoder.pcm {
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encoder.pcm[index] = int16(binary.LittleEndian.Uint16(
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pcm[index*2 : index*2+2],
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))
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}
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count, err := encoder.codec.EncodeInt16(encoder.pcm[:], encoder.packet[:])
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if err != nil {
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return nil, err
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}
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if count <= 0 || count > len(encoder.packet) {
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return nil, errors.New("native audio encoder returned an invalid packet")
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}
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return encoder.packet[:count], nil
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}
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