store song duration and length in state

src/components/beat-loader.js

@@ -97,6 +97,7 @@ AFRAME.registerComponent('beat-loader', {
    */
   handleBeats: function (beatData) {
     this.el.sceneEl.emit('beatloaderfinish', beatData, false);
+
     // Reset variables used during playback.
     // Beats spawn ahead of the song and get to the user in sync with the music.
     this.beatsTimeOffset = this.data.beatAnticipationTime * 1000;

src/components/song-preview.js

@@ -177,6 +177,8 @@ AFRAME.registerComponent('song-preview-system', {
     this.fadeIn();
     this.updateAnalyser();
 
+    this.el.sceneEl.emit('menuselectedchallengesonglength', this.audio.duration, false);
+
     // Prefetch buffer for playing.
     if (audioanalyser.xhr) { audioanalyser.xhr.abort(); }
     audioanalyser.fetchAudioBuffer(utils.getS3FileUrl(challengeId, 'song.ogg'));