ReplayGain support + audio normalization (web player) (#1988)

* ReplayGain support

- extract ReplayGain tags from files, expose via native api
- use metadata to normalize audio in web player

* make pre-push happy

* remove unnecessary prints

* remove another unnecessary print

* add tooltips, see metadata

* address comments, use settings instead

* remove console.log

* use better language for gain modes

scanner/mapping.go

@@ -75,6 +75,13 @@ func (s mediaFileMapper) toMediaFile(md metadata.Tags) model.MediaFile {
 	mf.CreatedAt = time.Now()
 	mf.UpdatedAt = md.ModificationTime()
 
+	if conf.Server.EnableReplayGain {
+		mf.RGAlbumGain = md.RGAlbumGain()
+		mf.RGAlbumPeak = md.RGAlbumPeak()
+		mf.RGTrackGain = md.RGTrackGain()
+		mf.RGTrackPeak = md.RGTrackPeak()
+	}
+
 	return *mf
 }
 

scanner/metadata/ffmpeg/ffmpeg_test.go

@@ -302,4 +302,23 @@ Input #0, mp3, from '/Users/deluan/Music/Music/Media/_/Wyclef Jean - From the Hu
 		md, _ := e.extractMetadata("tests/fixtures/test.ogg", output)
 		Expect(md).To(HaveKeyWithValue("fbpm", []string{"141.7"}))
 	})
+
+	It("parses replaygain data correctly", func() {
+		const output = `
+		Input #0, mp3, from 'test.mp3':
+			Metadata:
+				REPLAYGAIN_ALBUM_PEAK: 0.9125
+				REPLAYGAIN_TRACK_PEAK: 0.4512
+				REPLAYGAIN_TRACK_GAIN: -1.48 dB
+				REPLAYGAIN_ALBUM_GAIN: +3.21518 dB
+				Side data:
+					replaygain: track gain - -1.480000, track peak - 0.000011, album gain - 3.215180, album peak - 0.000021, 
+		`
+		md, _ := e.extractMetadata("tests/fixtures/test.mp3", output)
+		Expect(md).To(HaveKeyWithValue("replaygain_track_gain", []string{"-1.48 dB"}))
+		Expect(md).To(HaveKeyWithValue("replaygain_track_peak", []string{"0.4512"}))
+		Expect(md).To(HaveKeyWithValue("replaygain_album_gain", []string{"+3.21518 dB"}))
+		Expect(md).To(HaveKeyWithValue("replaygain_album_peak", []string{"0.9125"}))
+
+	})
 })

scanner/metadata/metadata.go

@@ -143,6 +143,39 @@ func (t Tags) Size() int64                 { return t.fileInfo.Size() }
 func (t Tags) FilePath() string            { return t.filePath }
 func (t Tags) Suffix() string              { return strings.ToLower(strings.TrimPrefix(path.Ext(t.filePath), ".")) }
 
+// Replaygain Properties
+func (t Tags) RGAlbumGain() float64 { return t.getGainValue("replaygain_album_gain") }
+func (t Tags) RGAlbumPeak() float64 { return t.getPeakValue("replaygain_album_peak") }
+func (t Tags) RGTrackGain() float64 { return t.getGainValue("replaygain_track_gain") }
+func (t Tags) RGTrackPeak() float64 { return t.getPeakValue("replaygain_track_peak") }
+
+func (t Tags) getGainValue(tagName string) float64 {
+	// Gain is in the form [-]a.bb dB
+	var tag = t.getFirstTagValue(tagName)
+
+	if tag == "" {
+		return 0
+	}
+
+	tag = strings.TrimSpace(strings.Replace(tag, "dB", "", 1))
+
+	var value, err = strconv.ParseFloat(tag, 64)
+	if err != nil {
+		return 0
+	}
+	return value
+}
+
+func (t Tags) getPeakValue(tagName string) float64 {
+	var tag = t.getFirstTagValue(tagName)
+	var value, err = strconv.ParseFloat(tag, 64)
+	if err != nil {
+		// A default of 1 for peak value resulds in no changes
+		return 1
+	}
+	return value
+}
+
 func (t Tags) getTags(tagNames ...string) []string {
 	for _, tag := range tagNames {
 		if v, ok := t.tags[tag]; ok {

scanner/metadata/metadata_test.go

@@ -41,6 +41,10 @@ var _ = Describe("Tags", func() {
 			Expect(m.FilePath()).To(Equal("tests/fixtures/test.mp3"))
 			Expect(m.Suffix()).To(Equal("mp3"))
 			Expect(m.Size()).To(Equal(int64(51876)))
+			Expect(m.RGAlbumGain()).To(Equal(3.21518))
+			Expect(m.RGAlbumPeak()).To(Equal(0.9125))
+			Expect(m.RGTrackGain()).To(Equal(-1.48))
+			Expect(m.RGTrackPeak()).To(Equal(0.4512))
 
 			m = mds["tests/fixtures/test.ogg"]
 			Expect(err).To(BeNil())