Implemented atomic session replacement.

cmd/mxl-player/playback_runtime.go

@@ -8,12 +8,19 @@ import (
 	"mxl-player/internal/playback"
 )
 
+type playerAudioSink interface {
+	playback.AudioSink
+	Close() error
+}
+
+var _ playerAudioSink = (*output.SDLAudioSink)(nil)
+
 type playerPlayback struct {
 	Controller *playback.SessionController
 	Commands   chan playback.SessionCommand
 	Video      *playback.VideoBridge
 	Status     *playback.StatusStore
-	Audio      *output.SDLAudioSink
+	Audio      playerAudioSink
 }
 
 func newPlayerPlayback(