feat: prefetch next track

cmd/daemon/controls.go

@@ -14,6 +14,48 @@ import (
 	"time"
 )
 
+func (p *AppPlayer) prefetchNext() {
+	next := p.state.tracks.PeekNext()
+	if next == nil {
+		return
+	}
+
+	nextId := librespot.SpotifyIdFromUri(next.Uri)
+	if p.secondaryStream != nil && p.secondaryStream.Is(nextId) {
+		return
+	}
+
+	log.Debugf("prefetching %s %s", nextId.Type(), nextId.Uri())
+
+	var err error
+	p.secondaryStream, err = p.player.NewStream(nextId, *p.app.cfg.Bitrate, 0)
+	if err != nil {
+		log.WithError(err).Warnf("failed prefetching stream for %s", nextId)
+		return
+	}
+
+	log.Infof("prefetched track \"%s\" (uri: %s, duration: %dms)",
+		p.primaryStream.Media.Name(), nextId.Uri(), p.primaryStream.Media.Duration())
+}
+
+func (p *AppPlayer) schedulePrefetchNext() {
+	if p.state.player.IsPaused || p.primaryStream == nil {
+		p.prefetchTimer.Reset(time.Duration(math.MaxInt64))
+		return
+	}
+
+	untilTrackEnd := time.Duration(p.primaryStream.Media.Duration()-int32(p.player.PositionMs())) * time.Millisecond
+	untilTrackEnd -= 30 * time.Second
+	if untilTrackEnd < 10*time.Second {
+		p.prefetchTimer.Reset(time.Duration(math.MaxInt64))
+
+		go p.prefetchNext()
+	} else {
+		p.prefetchTimer.Reset(untilTrackEnd)
+		log.Tracef("scheduling prefetch in %.0fs", untilTrackEnd.Seconds())
+	}
+}
+
 func (p *AppPlayer) handlePlayerEvent(ev *player.Event) {
 	switch ev.Type {
 	case player.EventTypePlaying:
@@ -185,6 +227,7 @@ func (p *AppPlayer) loadCurrentTrack(paused bool) error {
 	p.state.player.IsPlaying = true
 	p.state.player.IsBuffering = false
 	p.updateState()
+	p.schedulePrefetchNext()
 
 	p.app.server.Emit(&ApiEvent{
 		Type: ApiEventTypeMetadata,
@@ -253,13 +296,15 @@ func (p *AppPlayer) addToQueue(track *connectpb.ContextTrack) {
 	p.state.player.PrevTracks = p.state.tracks.PrevTracks()
 	p.state.player.NextTracks = p.state.tracks.NextTracks()
 	p.updateState()
+	p.schedulePrefetchNext()
 }
 
 func (p *AppPlayer) setQueue(prev []*connectpb.ContextTrack, next []*connectpb.ContextTrack) {
 	p.state.tracks.SetQueue(prev, next)
 	p.state.player.PrevTracks = p.state.tracks.PrevTracks()
 	p.state.player.NextTracks = p.state.tracks.NextTracks()
 	p.updateState()
+	p.schedulePrefetchNext()
 }
 
 func (p *AppPlayer) play() error {
@@ -283,6 +328,8 @@ func (p *AppPlayer) play() error {
 	p.state.player.PositionAsOfTimestamp = streamPos
 	p.state.player.IsPaused = false
 	p.updateState()
+	p.schedulePrefetchNext()
+
 	return nil
 }
 
@@ -300,6 +347,8 @@ func (p *AppPlayer) pause() error {
 	p.state.player.PositionAsOfTimestamp = streamPos
 	p.state.player.IsPaused = true
 	p.updateState()
+	p.schedulePrefetchNext()
+
 	return nil
 }
 
@@ -318,6 +367,7 @@ func (p *AppPlayer) seek(position int64) error {
 	p.state.player.Timestamp = time.Now().UnixMilli()
 	p.state.player.PositionAsOfTimestamp = position
 	p.updateState()
+	p.schedulePrefetchNext()
 
 	p.app.server.Emit(&ApiEvent{
 		Type: ApiEventTypeSeek,

cmd/daemon/main.go

@@ -13,6 +13,7 @@ import (
 	"go-librespot/zeroconf"
 	"golang.org/x/exp/rand"
 	"gopkg.in/yaml.v3"
+	"math"
 	"os"
 	"strings"
 	"time"
@@ -74,6 +75,9 @@ func (app *App) newAppPlayer(creds any) (_ *AppPlayer, err error) {
 		countryCode: new(string),
 	}
 
+	// start a dummy timer for prefetching next media
+	appPlayer.prefetchTimer = time.AfterFunc(time.Duration(math.MaxInt64), appPlayer.prefetchNext)
+
 	if appPlayer.sess, err = session.NewSessionFromOptions(&session.Options{
 		DeviceType:  app.deviceType,
 		DeviceId:    app.deviceId,

cmd/daemon/player.go

@@ -15,6 +15,7 @@ import (
 	"math"
 	"strings"
 	"sync"
+	"time"
 )
 
 type AppPlayer struct {
@@ -35,6 +36,8 @@ type AppPlayer struct {
 	state           *State
 	primaryStream   *player.Stream
 	secondaryStream *player.Stream
+
+	prefetchTimer *time.Timer
 }
 
 func (p *AppPlayer) handleAccesspointPacket(pktType ap.PacketType, payload []byte) error {
@@ -106,6 +109,8 @@ func (p *AppPlayer) handleDealerMessage(msg dealer.Message) error {
 			return fmt.Errorf("failed inactive state put: %w", err)
 		}
 
+		p.schedulePrefetchNext()
+
 		if p.app.cfg.ZeroconfEnabled {
 			p.logout <- p
 		}

tracks/tracks.go

@@ -156,6 +156,19 @@ func (tl *List) GoStart() bool {
 	return true
 }
 
+func (tl *List) PeekNext() *connectpb.ContextTrack {
+	if tl.playingQueue && len(tl.queue) > 1 {
+		return tl.queue[1]
+	}
+
+	iter := tl.tracks.iterHere()
+	if iter.next() {
+		return iter.get().item
+	}
+
+	return nil
+}
+
 func (tl *List) GoNext() bool {
 	if tl.playingQueue {
 		tl.queue = tl.queue[1:]