var xhr = new XMLHttpRequest();

     xhr.open('GET', '文件地址.mp4');

     xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

     xhr.responseType = "blob";

     xhr.onprogress = function (event) {

         if (event.lengthComputable) {

             console.log(event.loaded);

             console.log(event.total);         }

     };

     xhr.onload = function (oEvent) {

         console.log(oEvent);

         console.log(xhr.status);

         console.log(xhr.response);

         if (xhr.readyState === 4 && xhr.status === 200) {

             // var name = xhr.getResponseHeader("Content-disposition");

             // var filename = name.substring(20,name.length);

             var blob = new Blob([xhr.response], {type: 'video/mp4'});

             var csvUrl = URL.createObjectURL(blob);

             var link = document.createElement('a');

             link.href = csvUrl;

             link.download = 'abababababba.mp4';

             link.click();          

         }

     }

     xhr.send();