add ISO 15 equalizer implementation

player/player.go

@@ -113,6 +113,7 @@ type Player struct {
 	curPlaylistPos int64
 	prePausedState State
 	clientName     string
+	equalizer      Equalizer
 
 	bgCancel context.CancelFunc
 
@@ -501,6 +502,14 @@ func (p *Player) SetAudioDevice(deviceName string) error {
 	return p.mpv.SetPropertyString("audio-device", deviceName)
 }
 
+func (p *Player) SetEqualizer(eq Equalizer) error {
+	p.equalizer = eq
+	if eq == nil || !eq.IsEnabled() {
+		return p.mpv.SetPropertyString("af", "")
+	}
+	return p.mpv.SetPropertyString("af", eq.Curve().String())
+}
+
 func (p *Player) GetMediaInfo() (MediaInfo, error) {
 	var info MediaInfo
 	n, err := p.mpv.GetProperty("audio-params", mpv.FORMAT_NODE)