我是新人，请求帮助，请求大家帮我讲解下以下代码，先谢谢大家了,求知
if(!document.getElementByTagName){
atv.Document.prototype.getElementById = function(id)
{
var elements = this.evaluateXPath("//*[@id='" + id + "']", this);
return(elements && elements.length > 0) ? elements[0] : undefined;
};
atv.Element.prototype.getElementsByTagName = function(name)
{
return this.ownerDocument.evaluateXPath("descendant::" + name, this);
};
atv.Element.prototype.getElementByTagName = function(name)
{
var elements = this.getElementsByTagName(name);
return(elements && elements.length > 0) ? elements[0] : undefined;
};
}
function baseURL()
{
var src = document.rootElement.getElementByTagName("script").getAttribute('src');
return src.substring(0, src.lastIndexOf('/') + 1);
}
function makeXML(body, head)
{
var xml = '<?xml version="1.0" encoding="UTF-8"?><atv>' + (head ? ('<head>' + head + '</head>') : '') + '<body>' + body + '</body></atv>';
return atv.parseXML(xml);
}
function makeError(msg, desc)
{
return makeXML('<dialog id="error"><title><![CDATA[' + (msg || '') + ']]></title><description><![CDATA[' + (desc || '') + ']]></description></dialog>');
}
function quoteXML(s)
{
return s.replace(/[&<>'"]/g, function(c)
{
return "&" + {
"&": "amp",
"<": "lt",
">": "gt",
"'": "apos",
'"': "quot"
}[c] + ";"
})
}
function urlTitle(url)
{
var dir = (url.charAt(url.length - 1) == '/');
if(dir) url = url.substring(0, url.length - 1);
var title = decodeURIComponent(url.substring(url.lastIndexOf('/') + 1));
if(!dir)
{
var pos = title.lastIndexOf('.');
if(pos != -1)
{
title = title.substring(0, pos);
}
}
return title;
}
function decodeGBK(I)
{
O = '';
g = atv.localStorage['gbk'];
var i = 0;
while(i < I.length)
{
c = I[i];
i++;
h = c.charCodeAt(0);
if(h < 0x80)
{
O = O + c;
}
else
{
l = I.charCodeAt(i);
i++;
if(h >= 0xa1 && h <= 0xa9 && l >= 0xa1 && l <= 0xfe)
{
O = O + g.charAt((h - 0xa1) * 94 + (l - 0xa1));
}
else if(h >= 0xb0 && h <= 0xf7 && l >= 0xa1 && l <= 0xfe)
{
O = O + g.charAt((h - 0xb0) * 94 + (l - 0xa1) + 846);
}
else if(h >= 0x81 && h <= 0xA0 && l >= 0x40 && l <= 0xFE)
{
O = O + g.charAt((h - 0x81) * 190 + (l - 0x40) - (l > 0x7F ? 1 : 0) + 846 + 6768);
}
else if(h >= 0xAA && h <= 0xFE && l >= 0x40 && l <= 0xA0)
{
O = O + g.charAt((h - 0xAA) * 96 + (l - 0x40) - (l > 0x7F ? 1 : 0) + 846 + 6768 + 6080);
}
else if(h >= 0xA8 && h <= 0xA9 && l >= 0x40 && l <= 0xA0)
{
O = O + g.charAt((h - 0xA8) * 96 + (l - 0x40) - (l > 0x7F ? 1 : 0) + 846 + 6768 + 6080 + 8160);
}
}
}
return O;
}
function decodeBase64(I)
{
var k = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
O = "",
chr1, chr2, chr3 = "",
enc1, enc2, enc3, enc4 = "",
i = 0,
I = I.replace(/[^A-Za-z0-9\+\/\=]/g, "");
do {
enc1 = k.indexOf(I.charAt(i++));
enc2 = k.indexOf(I.charAt(i++));
enc3 = k.indexOf(I.charAt(i++));
enc4 = k.indexOf(I.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
O = O + String.fromCharCode(chr1);
if(enc3 != 64)
{
O = O + String.fromCharCode(chr2);
}
if(enc4 != 64)
{
O = O + String.fromCharCode(chr3);
}
chr1 = chr2 = chr3 = "";
enc1 = enc2 = enc3 = enc4 = "";
} while (i < I.length);
return unescape(O);
}
function httpRequest(url, callback, body, headers, utf8)
{
var req = new XMLHttpRequest();
req.onreadystatechange = function()
{
try
{
if(req.readyState == 4)
{
if(req.status == 200)
{
var text = req.responseText;
if(!text & req.responseDataAsBase64.length > 0)
{
g = atv.localStorage['gbk'];
if(!g)
{
httpRequest(baseURL() + 'gbk.txt', function(res)
{
atv.localStorage['gbk'] = res;
if(utf8 == 1) text = decodeBase64(req.responseDataAsBase64);
else text = decodeGBK(decodeBase64(req.responseDataAsBase64));
if(callback) callback(text);
});
return;
};
if(utf8 == 1) text = decodeBase64(req.responseDataAsBase64);
else text = decodeGBK(decodeBase64(req.responseDataAsBase64));
};
if(callback) callback(text);
}
else
{
if(callback) callback();
}
}
}
catch(e)
{
req.abort();
if(callback) callback();
}
};
req.open((body ? "POST" : "GET"), url, true);
if(headers) for(var key in headers) req.setRequestHeader(key, headers[key]);
req.send(body);
return req;
};
function playItem(url, list_count, sub_count)
{
var desc = '文件位置：' + decodeURIComponent(url);
if(sub_count) desc += '\n' + '外挂字幕：' + sub_count + ' 句';
if(list_count) desc += '\n' + '播放列表：' + list_count + ' 项';
var item = {
type: 'video-asset',
'media-asset': {
'media-url': url,
type: 'http-live-streaming',
title: urlTitle(url),
description: desc,
}
};
return item;
}
function playFile(url, list, sub)
{
var item = playItem(url, list ? (list.length + 1) : 0, sub ? (sub.length + 1) : 0);
if(sub && sub.length) item['subtitle'] = sub;
if(list && list.length) item['playlist'] = list;
atv.loadPlist(item);
}
function loadFile(url, list)
{
function subt(sts)
{
var sa = sts.split(',');
var sec = sa[0];
if(sa.length > 1)
{
ml = parseInt(sa[1], 10);
}
else ml = 0;
ta = sec.split(':');
if(ta.length == 3)
{
secs = parseInt(ta[0], 10) * 3600 + parseInt(ta[1], 10) * 60 + parseInt(ta[2], 10);
}
else if(ta.length == 2)
{
secs = parseInt(ta[0], 10) * 60 + parseInt(ta[1], 10);
}
else secs = parseInt(ta[0], 10);
return secs + (ml / 1000.0);
};
var pos = url.lastIndexOf('.');
var key = url.substring(0, pos);
var srtlist = atv.sessionStorage['srtlist'];
for(var i in srtlist)
{
var srt = srtlist[i];
if((pos < srt.length) && (key == srt.substring(0, pos)))
{
httpRequest(srt, function(res)
{
var sub = [];
if(res)
{
var lines = res.replace(/\r/g, '').split('\n\n');
for(var i = 0; i < lines.length; i++)
{
var subline = lines[i].split('\n');
var subid = subline.shift();
if(!subid) continue;
var subtime = subline.shift();
if(!subtime) continue;
var sta = subtime.split('-->');
var startt = subt(sta[0]);
var endt = subt(sta[1]);
var subinfo = subline.join('\n').replace('\\N', '\n');
sub.push([subid, startt, endt, subinfo]);
}
}
playFile(url, list, sub);
});
return;
}
}
playFile(url, list);
}
function loadFiles(url)
{
var playlist = [];
var behind = false;
var filelist = atv.sessionStorage['filelist'];
for(var i in filelist)
{
if(behind)
{
playlist.push(playItem(filelist[i], filelist.length - i));
}
else if(filelist[i] === url)
{
behind = true;
}
}
loadFile(url, playlist);
}
function makeMedia(url, text)
{
//
var sbase = baseURL();
var base = url.substring(0, url.lastIndexOf('/') + 1);
var host = url.substring(0, url.indexOf('/', 8));
//
var srtlist = [];
var filelist = [];
var posters = '';
var photos = '';
var posters_count = 0;
var photos_count = 0;
if(text != null)
{
// Split text to blocks
var blocks = text.split('</tr>');
if(blocks.length < 2) blocks = text.split('</li>');
if(blocks.length < 2) blocks = text.split('<br>');
if(blocks.length < 2) blocks = text.split('\n');
// Parse dir, file or thumb items
var dirs = [];
var files = [];
var thumbs = [];
for(var i in blocks)
{
var re = new RegExp('<a href="(.*?)">(.*?)</a>', 'i');
var rs = re.exec(blocks[i]);
if(rs)
{
var href = rs[1];
if(href.indexOf(':') == -1)
{
if(href.charAt(0) == '/') href = host + href;
else href = base + href;
}
if(href.indexOf('.thumb.') != -1)
{
thumbs.push(href);
}
else
{
var name = rs[2].replace(/^\s+/, '').replace(/\s+$/, ''); // Trim prefix and sufix space
if((name.charAt(0) != '.') && (name.indexOf('Parent Directory') == -1))
{
if(href.charAt(href.length - 1) == '/')
{
dirs.push([href, name]);
}
else
{
files.push([href, name]);
}
}
}
}
}
var nothumb = false;
function fetchThumb(thumbs, sbase, href, type)
{
// Fetch image
var pos = href.lastIndexOf('/');
var key = (pos != -1) ? href.substring(pos + 1) : href;
for(var i in thumbs)
{
if(thumbs[i].indexOf(key) != -1)
{
return thumbs[i];
}
}
if(type != 'dir') nothumb = true;
return type ? (sbase + 'image/' + type + '.png') : href;
}
function makePoster(thumbs, sbase, id, name, href, type, play, select)
{
// Make poster
poster = '<moviePoster alwaysShowTitles="true" id="' + type + id + '" onPlay="' + play + '" onSelect="' + select + '">';
poster += '<title>' + quoteXML(name) + '</title>';
poster += '<image>' + quoteXML(fetchThumb(thumbs, sbase, href, type)) + '</image>';
poster += '<defaultImage>resource://Poster.png</defaultImage>';
poster += '</moviePoster>';
return poster;
}
// Make dir item
for(var i in dirs)
{
var href = dirs[i][0];
var name = dirs[i][1];
var action = 'loadPage(\'' + quoteXML(href) + '\')';
if(name.charAt(name.length - 1) == '/') name = name.substring(0, name.length - 1);
posters += makePoster(thumbs, sbase, ++posters_count, name, href.substring(0, href.length - 1), 'dir', action, action);
}
// Make file item
for(var i in files)
{
var href = files[i][0];
var name = files[i][1];
var type = href.substring(href.lastIndexOf('.') + 1).toLowerCase();
if(type == 'mov' || type == 'mp4' || type == 'm4v' || type == 'mkv' || type == 'mpg' || type == 'avi' || type == 'm3u' || type == 'mp3' || type == 'aac')
{
filelist.push(href);
var pos = name.lastIndexOf('.');
if(pos != -1) name = name.substring(0, pos);
var play = 'loadFiles(\'' + quoteXML(href) + '\')';
var select = 'loadFile(\'' + quoteXML(href) + '\')';
posters += makePoster(thumbs, sbase, ++posters_count, name, href, type, play, select);
}
else if(type == 'jpg' || type == 'png' || type == 'gif' || type == 'bmp')
{
var id = type + ++photos_count;
photos += '<photo id="' + id + '" onSelect="onPhotoSelection(\'' + id + '\')" onPlay="onSlideshowStart(\'' + id + '\')">';
photos += '<assets><photoAsset width="0" height="0" src="' + quoteXML(fetchThumb(thumbs, sbase, href)) + '"/></assets>';
photos += '</photo>';
}
else if(type == 'srt')
{
srtlist.push(href);
}
}
// Request for thumbnail on server
if(nothumb)
{
var uri = url.substring(url.indexOf('/', 8) + 1);
var pos = uri.indexOf('?');
if(pos != -1) uri = uri.substring(0, pos);
pos = uri.indexOf('#');
if(pos != -1) uri = uri.substring(0, pos);
httpRequest(sbase + 'thumb.cgi?' + uri);
}
}
atv.sessionStorage['srtlist'] = srtlist;
atv.sessionStorage['filelist'] = filelist;
//
if(photos_count == 0 && posters_count == 0)
{
return makeError('没有内容', decodeURIComponent(url));
}
// Geenrate XML
var body;
var head = '<script id="media.js" src="' + sbase + 'media.js"/>';
if(photos_count > posters_count)
{
head += '<script src="' + sbase + 'slide.js"/>';
body = '<mediaBrowser id="browser" gridLayout="mixed">';
body += '<header><headerWithCountAndButtons><title>' + urlTitle(url) + '</title><count>' + photos_count + '</count>';
body += '<buttons><actionButton id="slideshow" onSelect="onSettingsSelection()" onPlay="onSlideshowStart()"><title>幻灯片播放</title></actionButton></buttons>';
body += '</headerWithCountAndButtons></header><items>' + photos + '</items></mediaBrowser>';
}
else
{
body = '<scroller id="scroller"><items><grid columnCount="5" id="grid"><items>' + posters + '</items></grid></items></scroller>';
}
return makeXML(body, head);
}
function loadDoc(doc, event)
{
if(event) event.success(doc);
else atv.loadXML(doc);
}
function loadPage(url, event)
{
var req = new XMLHttpRequest();
req.onreadystatechange = function()
{
try
{
if(req.readyState == 4)
{
loadDoc((req.status == 200) ? ((url.indexOf('.xml') != -1) ? req.responseXML : makeMedia(url, req.responseText)) : makeError('状态错误：' + req.status, url), event);
}
}
catch(e)
{
req.abort();
loadDoc(makeError(e, url), event);
}
}
req.open('GET', url, true);
req.send();
}
function loadItem(event)
{
var id = event.navigationItemId;
var item = document.getElementById(id);
var url = item.getElementByTagName('url').textContent;
loadPage(url, event);
}
