Added a duration field to Song_ struct.

internal/radio/song.go

@@ -11,6 +11,7 @@ import (
 type Song_ struct {
 	Artist       string
 	Title        string
+	Duration     time.Duration
 	MaxListeners int
 	StartAt      time.Time
 }
@@ -23,11 +24,13 @@ func (s *Song_) MarshalJSON() ([]byte, error) {
 	return json.Marshal(&struct {
 		Artist       string `json:"artist"`
 		Title        string `json:"title"`
+		Duration     int64  `json:"duration_milliseconds"`
 		MaxListeners int    `json:"listeners"`
 		StartAt      string `json:"start_at"`
 	}{
 		Artist:       s.Artist,
 		Title:        s.Title,
+		Duration:     s.Duration.Milliseconds(),
 		MaxListeners: s.MaxListeners,
 		StartAt:      s.StartAt.UTC().Format(time.RFC3339)})
 }