downloadFile下载问题

downloadfile，下载视频号视频的时候，进度条，数据长度这些都是乱的
链接
http://51.wxapp.tc.qq.com/251/20302/stodownload?hy=SH&m=&pcdnfilekey=Cvvj5Ix3eewK0tHtibORqcsqchXNh0Gf3sJcaYqC2rQAficXwKhpLdgiafYZa8KIM9FS4opu0gm6HQFpqrH95AoEv5xmRbljG8AyB1mib9py4SWUMdqU2RxiaePGiaibibMLmGvM&pcdntoken=749LOwRsVf9wc2XWDPsWV4Xp7AJQibddS32s4iaWrg4gyicvM3LnCriaz5ISmOT8Qg4b&taskid=7d2abcc98357c739&tokenidx=1&uzid=2