var options = {            // controls: 'control',            controls: false,            preload: 'auto',            playsinline: true,            poster: "http://shortmeetadmin.oss-cn-beijing.aliyuncs.com/1515394799463",        };        var player = videojs('video', options, function onPlayerReady() {            videojs.log('Your player is ready!');            this.play();                      console.log(this.duration())    //總是 NaN        });https://github.com/videojs/vi...http://docs.videojs.com/tutor...