It may not play in the browser, but streamlink works.
Code:
streamlink "hls://http://pl.koolearn.com/video/m3u8_free?id=16918&consumerType=1002001&userId=-1&keyNumber=0001×Tamp=?????????????&key=????????????????????????????????&hiddenTeach=1" best -o 2015_ys_yd_5-6_ybn_16.ts