feat: add OpusConfig and encoder options (bitrate, complexity, FEC)

Adds OpusEncodeOptions and OpusConfig so deployments can tune bitrate,
complexity, and FEC without rebuilding. Encoder option application is
stubbed pending livekit/media-sdk#69 (EncodeWith).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thetillhoff

pkg/config/config.go

@@ -44,6 +44,15 @@ var (
 	DefaultRTPPortRange = rtcconfig.PortRange{Start: 10000, End: 20000}
 )
 
+// OpusConfig tunes the Opus encoder for SIP media. All fields are optional;
+// zero values keep libopus defaults.
+type OpusConfig struct {
+	Bitrate           int  `yaml:"bitrate"`             // target bitrate in bits/sec (e.g. 24000); 0 = auto
+	Complexity        int  `yaml:"complexity"`          // encoder complexity 1-10; 0 = default
+	FEC               bool `yaml:"fec"`                 // enable in-band Forward Error Correction
+	PacketLossPercent int  `yaml:"packet_loss_percent"` // expected packet loss 0-100, tunes FEC
+}
+
 type TLSCert struct {
 	CertFile string `yaml:"cert_file"`
 	KeyFile  string `yaml:"key_file"`
@@ -112,6 +121,7 @@ type Config struct {
 	IgnoreLocalAddrInSDP bool            `yaml:"ignore_local_addr_in_sdp"` // enable symmetric RTP if local IP is specified in SDP
 	Codecs               map[string]bool `yaml:"codecs"`
 	EnableOpus           bool            `yaml:"enable_opus"`
+	Opus                 OpusConfig      `yaml:"opus"`
 
 	// HideInboundPort controls how SIP endpoint responds to unverified inbound requests.
 	// Setting it to true makes SIP server silently drop INVITE requests if it gets a negative Auth or Dispatch response.

pkg/sip/media_codecs_opus.go

@@ -17,11 +17,21 @@
 package sip
 
 import (
+	"sync/atomic"
+
 	msdk "github.com/livekit/media-sdk"
 	"github.com/livekit/media-sdk/opus"
 	"github.com/livekit/protocol/logger"
 )
 
+var opusEncodeOpts atomic.Pointer[OpusEncodeOptions]
+
+// SetOpusOptions configures the Opus encoder. Call before or after enabling;
+// takes effect on the next encoder instantiation (i.e. next call).
+func SetOpusOptions(opts OpusEncodeOptions) {
+	opusEncodeOpts.Store(&opts)
+}
+
 func init() {
 	msdk.RegisterCodec(msdk.NewAudioCodec(msdk.CodecInfo{
 		SDPName:      OpusSDPName,
@@ -51,6 +61,7 @@ func opusDecode(w msdk.PCM16Writer) msdk.WriteCloser[opus.Sample] {
 }
 
 func opusEncode(w msdk.WriteCloser[opus.Sample]) msdk.PCM16Writer {
+	// TODO: apply opusEncodeOpts once livekit/media-sdk#69 (EncodeWith) merges.
 	enc, err := opus.Encode(w, 1, logger.GetLogger())
 	if err != nil {
 		logger.GetLogger().Errorw("opus encode init failed", err)

pkg/sip/media_codecs_opus_nocgo.go

@@ -18,3 +18,6 @@ package sip
 
 // SetOpusEnabled is a no-op in non-CGo builds; Opus requires libopus.
 func SetOpusEnabled(_ bool) {}
+
+// SetOpusOptions is a no-op in non-CGo builds; Opus requires libopus.
+func SetOpusOptions(_ OpusEncodeOptions) {}

pkg/sip/service.go

@@ -217,6 +217,14 @@ func (s *Service) Start() error {
 	}
 	msdk.CodecsSetEnabled(s.conf.Codecs)
 	SetOpusEnabled(s.conf.EnableOpus)
+	if s.conf.EnableOpus {
+		SetOpusOptions(OpusEncodeOptions{
+			Bitrate:           s.conf.Opus.Bitrate,
+			Complexity:        s.conf.Opus.Complexity,
+			FEC:               s.conf.Opus.FEC,
+			PacketLossPercent: s.conf.Opus.PacketLossPercent,
+		})
+	}
 
 	if err := s.mon.Start(s.conf); err != nil {
 		return err