expose MPV ReplayGain options

player/libmpv.go

@@ -104,6 +104,14 @@ func (m libmpv) SetProperty(name string, format MPVFormat, value any) error {
 	return toMPVError(C.mpv_set_property(m.handle, cname, C.mpv_format(format), p))
 }
 
+func (m libmpv) SetPropertyString(name, value string) error {
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+	cvalue := C.CString(value)
+	defer C.free(unsafe.Pointer(cvalue))
+	return toMPVError(C.mpv_set_property_string(m.handle, cname, cvalue))
+}
+
 func (m libmpv) GetProperty(name string, format MPVFormat) (any, error) {
 	cname := C.CString(name)
 	defer C.free(unsafe.Pointer(cname))

player/player.go

@@ -38,12 +38,30 @@ const (
 	SeekRelativePercent
 )
 
+// One of "no", "track", or "album"
+type ReplayGainMode string
+
+const (
+	ReplayGainNone  ReplayGainMode = "no"
+	ReplayGainTrack ReplayGainMode = "track"
+	ReplayGainAlbum ReplayGainMode = "album"
+)
+
+// Replay Gain options (argument to SetReplayGainOptions).
+type ReplayGainOptions struct {
+	Mode         ReplayGainMode
+	FallbackGain float64
+	PreampGain   float64
+}
+
 // Player encapsulates the mpv instance and provides functions
 // to control it and to check its status.
 type Player struct {
 	mpv            libmpv
 	initialized    bool
 	vol            int
+	replayGainOpts ReplayGainOptions
+	haveRGainOpts  bool
 	status         Status
 	seeking        bool
 	curPlaylistPos int64
@@ -99,6 +117,9 @@ func (p *Player) Init(audioExclusive bool) error {
 		if audioExclusive {
 			m.SetOptionString("audio-exclusive", "yes")
 		}
+		if p.haveRGainOpts {
+			p.SetReplayGainOptions(p.replayGainOpts)
+		}
 
 		if p.clientName != "" {
 			m.SetOptionString("audio-client-name", p.clientName)
@@ -232,6 +253,26 @@ func (p *Player) SetVolume(vol int) error {
 	return nil
 }
 
+// Sets the ReplayGain options of the player.
+// Unlike most Player functions, SetReplayGainOptions can be called
+// before Init, to set the initial volume of the player on startup.
+func (p *Player) SetReplayGainOptions(options ReplayGainOptions) error {
+	p.replayGainOpts = options
+	p.haveRGainOpts = true
+	if p.initialized {
+		if err := p.mpv.SetPropertyString("replaygain", string(options.Mode)); err != nil {
+			return err
+		}
+		if err := p.mpv.SetProperty("replaygain-preamp", MPVFormatDouble, options.PreampGain); err != nil {
+			return err
+		}
+		if err := p.mpv.SetProperty("replaygain-fallback", MPVFormatDouble, options.FallbackGain); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // Gets the current volume of the player.
 func (p *Player) GetVolume() int {
 	return p.vol