Improve seeking with big output device buffers

cmd/daemon/controls.go

@@ -175,11 +175,11 @@ func (s *Session) pause() error {
 		return fmt.Errorf("no stream")
 	}
 
-	s.stream.Pause()
-
 	streamPos := s.stream.PositionMs()
 	log.Debugf("pause track at %dms", streamPos)
 
+	s.stream.Pause()
+
 	s.state.playerState.Timestamp = time.Now().UnixMilli()
 	s.state.playerState.PositionAsOfTimestamp = streamPos
 	s.state.playerState.IsPaused = true

output/driver_unix.go

@@ -242,6 +242,42 @@ func (out *output) Resume() error {
 	return nil
 }
 
+func (out *output) Drop() error {
+	out.cond.L.Lock()
+	defer out.cond.L.Unlock()
+
+	if out.closed || out.released {
+		return nil
+	}
+
+	if err := C.snd_pcm_drop(out.handle); err < 0 {
+		return alsaError("snd_pcm_drop", err)
+	}
+
+	// since we are not actually stopping the stream, prepare it again
+	if err := C.snd_pcm_prepare(out.handle); err < 0 {
+		return alsaError("snd_pcm_prepare", err)
+	}
+
+	return nil
+}
+
+func (out *output) DelayMs() (int64, error) {
+	out.cond.L.Lock()
+	defer out.cond.L.Unlock()
+
+	if out.closed || out.released {
+		return 0, nil
+	}
+
+	var frames C.snd_pcm_sframes_t
+	if err := C.snd_pcm_delay(out.handle, &frames); err < 0 {
+		return 0, alsaError("snd_pcm_delay", err)
+	}
+
+	return int64(frames) * 1000 / int64(out.sampleRate), nil
+}
+
 func (out *output) SetVolume(vol float32) {
 	if vol < 0 || vol > 1 {
 		panic(fmt.Sprintf("invalid volume value: %0.2f", vol))

output/output.go

@@ -57,6 +57,16 @@ func (c *Output) Resume() error {
 	return c.output.Resume()
 }
 
+// Drop empties the audio buffer without waiting.
+func (c *Output) Drop() error {
+	return c.output.Drop()
+}
+
+// DelayMs returns the output device delay in milliseconds.
+func (c *Output) DelayMs() (int64, error) {
+	return c.output.DelayMs()
+}
+
 // SetVolume sets the volume (0-1).
 func (c *Output) SetVolume(vol float32) {
 	c.output.SetVolume(vol)

player/player.go

@@ -143,15 +143,26 @@ loop:
 				cmd.resp <- struct{}{}
 				p.ev <- Event{Type: EventTypeStopped}
 			case playerCmdSeek:
-				if source != nil {
-					err := source.SetPositionMs(cmd.data.(int64))
-					cmd.resp <- err
+				if source != nil && out != nil {
+					if err := source.SetPositionMs(cmd.data.(int64)); err != nil {
+						cmd.resp <- err
+					} else if err := out.Drop(); err != nil {
+						cmd.resp <- err
+					} else {
+						cmd.resp <- nil
+					}
 				} else {
 					cmd.resp <- nil
 				}
 			case playerCmdPosition:
-				if source != nil {
-					cmd.resp <- source.PositionMs()
+				if source != nil && out != nil {
+					delay, err := out.DelayMs()
+					if err != nil {
+						log.WithError(err).Warnf("failed getting output device delay")
+						delay = 0
+					}
+
+					cmd.resp <- source.PositionMs() - delay
 				} else {
 					cmd.resp <- int64(0)
 				}

vorbis/decoder.go

@@ -366,10 +366,10 @@ func (d *Decoder) SetPositionMs(pos int64) (err error) {
 		}
 	}
 
+	d.buf = nil
 	return nil
 }
 
 func (d *Decoder) PositionMs() int64 {
-	// TODO: account for alsa delay with snd_pcm_delay
 	return int64(vorbis.GranuleTime(&d.dspState, d.lastGranulepos) * 1000)
 }