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

ui/src/common/SongInfo.js

@@ -17,15 +17,21 @@ import inflection from 'inflection'
 import { BitrateField, SizeField } from './index'
 import { MultiLineTextField } from './MultiLineTextField'
 import { makeStyles } from '@material-ui/core/styles'
+import config from '../config'
 
 const useStyles = makeStyles({
+  gain: {
+    '&:after': {
+      content: (props) => (props.gain ? " ' db'" : ''),
+    },
+  },
   tableCell: {
     width: '17.5%',
   },
 })
 
 export const SongInfo = (props) => {
-  const classes = useStyles()
+  const classes = useStyles({ gain: config.enableReplayGain })
   const translate = useTranslate()
   const record = useRecordContext(props)
   const data = {
@@ -54,6 +60,15 @@ export const SongInfo = (props) => {
     data.playDate = <DateField record={record} source="playDate" showTime />
   }
 
+  if (config.enableReplayGain) {
+    data.albumGain = (
+      <NumberField source="rgAlbumGain" className={classes.gain} />
+    )
+    data.trackGain = (
+      <NumberField source="rgTrackGain" className={classes.gain} />
+    )
+  }
+
   return (
     <TableContainer>
       <Table aria-label="song details" size="small">