Unsuccessful XHR Library on OGG over HTTP Live Stream

gistfile1.js

// vim: set et sw=2 ts=2 sts=2 ff=unix fenc=utf8:
// Author: Binux<i@binux.me>
//         http://binux.me
//		   acgrid<acgrid@gmail.com>
// Created on 2013-04-20 20:17:45

define(['underscore', 'utils', 'jquery'], function(__,utils,$) {

  return {
    choice_piece_size: function() {
      var psize = 1 << 19; // 1M, 4M for production
      return psize;
    },

    choice_block_size: function(piece_size) {
      var bsize = piece_size;
      while (bsize > 1 << 18) { // 512K, 1M for production
        bsize >>= 1;
      }
      return bsize;
    },

    build: function(stream_url) {
      var piece_size = this.choice_piece_size();
      var block_size = this.choice_block_size(piece_size);
      var result = {
        type: utils.source_mimetype(stream_url),
        piece_size: piece_size,
        piece_cnt: 0,
        block_size: block_size,
      };

      var builder = {
        'result': result
      };
      return builder;
    },
	
	loop: function(stream_url, piece_size, onrecv, ondata) {
		var last_size = 0;
		var first = 2;
		try{
			var xhr = new XMLHttpRequest();
			xhr.responseType = 'stream';
			//xhr.overrideMimeType('text/plain; charset=x-user-define'); 
			
			xhr.onerror = function() { console.log(e); };
			xhr.addEventListener("progress", function(evt) {
				//$("#J_ajax_size").text(utils.format_size(evt.loaded)); // for test, also console.log(evt.loaded)
			}, false);
			
			xhr.onreadystatechange = function() {
				try{
					if (xhr.readyState == xhr.LOADING){
						if(first > 0){
							console.log(this.response); 
							console.log(typeof(this.response)); // result: string
							console.log(this.response.length);
							console.log(this.responseText.length);
							first--;
						}
						var blob = new Blob([this.response],{type: "video/ogg"});
						var total_size = blob.size;
						var offset = last_size;
						if (_.isFunction(onrecv)) {
							onrecv(total_size);
						}
						if(total_size > last_size && last_size + piece_size < total_size){ // new data arrive and can fill up a new block, do write add callback update
							last_size = total_size; // Consider possible disorder: late blocks is written before early blocks
							if (_.isFunction(ondata)) {
								var thisblob = blob.slice(offset,blob.size);
								ondata(thisblob,offset,last_size);
							}
						}
					}   
				}catch (e){
					console.log(e);
				}
			};
	 
			xhr.open("GET", stream_url, true);
			xhr.send();      
		}catch (e){
			console.log(e);
		}
	}
  };
});