用python做youtube自動化下載器 思路
阿新 • • 發佈：2021-01-11
目錄
我們就可以確定關於下載連結會出現在這個請求的返回值內。-EOF-
根據 savefrom條例
本例項及教程只用於學習交流用，權利歸savefrom.net所有
0. 思路
使用python從savefrom平臺上獲取指定youtube視訊下載連結進行下載，不過savefrom的資料是用javascript加密的，這也是難度所在
本教程主要介紹製作思路，下一篇會介紹製作python
本教程根據stakoverflow 回答製作
1.準備
i.savfrom.net
一個網站可以免費下載youtube視訊
2. 探索並規劃獲取方式
i.總覽
開啟https://en.savefrom.net/1-youtube-video-downloader-4/可以看見頁面主要就一個from表單輸入框和提交按鈕組成
ii. 獲取該網頁取到下載url的請求
在chrome或其他瀏覽器按F12開啟開發者控制檯，點開Network選項卡
接下來模擬正常的使用者流程，在輸入框輸入一個youtube視訊地址，比如這個https://www.youtube.com/watch?v=IjJmTeBSEzU，然後點選Download提交url獲取下載url，然後我們可以發現下面已經出現了下載連結。然後我們在network選項卡內可以發現一個特殊的申請saveform.php
savform.php)我們就可以確定關於下載連結會出現在這個請求的返回值內。
iii. 在本地獲取請求
在本地用IDE的http工具或者python構建出post請求程式碼，筆者用的是pycharm的httpClient(按2下左Shift，然後輸入Tools，然後回車進入選單，然後點選httpClient下的第一個)
把請求裡第二個headers的內容全部複製然後格式化然後構建post請求
然後把下面的formdata的引數也複製進來，記得和headers換行
POST https://en.savefrom.net/savefrom.php cache-Control: no-cache accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9 accept-encoding: gzip, deflate, br accept-language: zh-CN,zh;q=0.9,en;q=0.8 content-type: application/x-www-form-urlencoded cookie: lang=en; country=CN; uid=fd94a82a406a8dd4; sfHelperDist=72; reference=14; clickads-e2=90; poropellerAdsPush-e=63; promoBlock=64; helperWidget=92; helperBanner=42; framelessHdConverter=68; inpagePush2=68; popupInOutput=9; _ga=GA1.2.799702638.1610248969; _gid=GA1.2.628904587.1610248969; PHPSESSID=4aojkm49oj7h3de65pekqii337; x-requested-with=; PHPSESSUD=122fb7e10af37e23d99e896fd188744f; _gat_helperWidget=1; _gat_inpagePush2=1 origin: https://en.savefrom.net pragma: no-cache referer: https://en.savefrom.net/1-youtube-video-downloader-4/ sec-ch-ua: "Google Chrome";v="87", " Not;A Brand";v="99", "Chromium";v="87" sec-ch-ua-mobile: ?0 sec-fetch-dest: iframe sec-fetch-mode: navigate sec-fetch-site: same-origin sec-fetch-user: ?1 upgrade-insecure-requests: 1 user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36 sf_url=https://www.youtube.com/watch?v=YPvtz1lHRiw&sf_submit=&new=1&lang=en&app=&country=cn&os=Windows&browser=Chrome
如果配置沒錯，這個時候你執行後會顯示出和在瀏覽器裡一樣的結果，然後可以發現引數裡的sf_url就是需要下載的youtube地址
iv.解析請求結果
把取到的結果儲存在本地然後在瀏覽器開啟儲存的本地檔案，然後彈出一個彈窗後會發現這個頁面什麼都沒有，但其實如果你在console輸入window會發現有很多變數和函式，其中就有我們需要的加密後的url和解密函式
經過彈窗提示我們可以發現是這個html的js發現了我們不在他的網站上然後刪除了顯示下載url的程式碼所以我們才什麼都看不到，開啟source選項卡或者用IDE開啟原始碼檢視
掃一下這個原始碼，我們可以看見一些加密解密函式，被加密的亂碼資訊，雜湊對照表，和一些奇怪的賦值操作，如圖
我們可以看見，js部分由一個大閉包組成
- 第3行到第9行是宣告函式
- 第10行是給
$b賦值this也就是window - 第11到第13行是賦值3個變數
- 第14，15行是對變數執行一些操作，這個也是我們重點關注的，畢竟執行加密，解密方法只可能在這
第14，15行格式化後如下
this.$d = $d;
this.$a = $a;
this.$e = $e;
this.$k = $k;
this.$c = $c;
$c = _q($c);
$c = _b($c);
_m($b, $c);
去掉前5行沒有意義的變數互換值，加密解密函式存在的範圍就在最後3行
$c = _q($c);
$c = _b($c);
_m($b, $c);
然後開始一個個試
先在console裡輸入第一行
然後就出現了明文，所以我們就確定這個是我們需要的解密函式
接下來輸入第二行
發現出現了和上面一模一樣的明文，所以這個也是解密函式
接下來輸入第三行
發現這個執行了那段程式碼，這個應該是執行函式，所以我們現在就找到了解密函式位於js部分的最後幾行
v.解析解密後的結果
把console裡用解密函式解密出的結果複製出來會得到一個JavaScript指令碼
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})();
我們可以發現裡面有個del()刪除函式，這就是為什麼我們看不到這一段程式碼在執行後
因為被window.location.hostname.search(/(?:^|\.|@)(savefrom\.net|sfrom\.net|savefrom\.com\.au|51\.159\.57\.158|(?:fe\d*|test)-front\.sf-apps\.com)$/i) == -1檢查出不是在他的網站上跑的所以就執行彈窗和del()把解密後的東西刪除了
仔細檢查這段程式碼可以發現這一行
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這裡面有一長串json文字然後裡面就包含我們要的下載連結和其他雜七雜八的東西，在json格式化平臺(比如bejson)把這一段json文字輸入
可以發現meta主要是視訊訊息，然後url下就是不同解析度的視訊下載連結了
下一章會講怎麼製作自動python程式