背景音频问题

 var  backgroundAudioManager = wx.getBackgroundAudioManager()

backgroundAudioManager.title = ‘此时此刻’

backgroundAudioManager.src = ‘http://www.wujianglong.com.cn/other/m.mp3’ 

背景音频开始播放  在设置 wx.backgroundAudio.seek({position:50})   报Cannot read property ‘seek’ of undefined;at “pages/swiper/swiper” page lifeCycleMethod onLoad function错误，求大神指导  背景音频wx.getBackgroundAudioManager()与wx.playBackgroundAudio(OBJECT)区别是什么