Add support xiaomi source

pkg/xiaomi/backchannel.go

@@ -0,0 +1,42 @@
+package xiaomi
+
+import (
+	"time"
+
+	"github.com/AlexxIT/go2rtc/pkg/core"
+	"github.com/AlexxIT/go2rtc/pkg/xiaomi/miss"
+	"github.com/pion/rtp"
+)
+
+const size8bit40ms = 8000 * 0.040
+
+func (p *Producer) AddTrack(media *core.Media, _ *core.Codec, track *core.Receiver) error {
+	if err := p.client.SpeakerStart(); err != nil {
+		return err
+	}
+	// TODO: check this!!!
+	time.Sleep(time.Second)
+
+	sender := core.NewSender(media, track.Codec)
+
+	switch track.Codec.Name {
+	case core.CodecPCMA:
+		var buf []byte
+
+		sender.Handler = func(pkt *rtp.Packet) {
+			buf = append(buf, pkt.Payload...)
+			for len(buf) >= size8bit40ms {
+				_ = p.client.WriteAudio(miss.CodecPCMA, buf[:size8bit40ms])
+				buf = buf[size8bit40ms:]
+			}
+		}
+	case core.CodecOpus:
+		sender.Handler = func(pkt *rtp.Packet) {
+			_ = p.client.WriteAudio(miss.CodecOPUS, pkt.Payload)
+		}
+	}
+
+	sender.HandleRTP(track)
+	p.Senders = append(p.Senders, sender)
+	return nil
+}