根据 savefrom条例

本实例及教程只用于学习交流用，权利归savefrom.net所有

最后代码+注释大概100行左右，具体代码以github代码为主(可以会在上面修复bug)，本文只做具体讲解

项目地址

github仓库

思路

用python做youtube自动化下载器 思路

流程

1. post

根据思路里的第一步，我们首先需要用post方式取到加密后的js字段，笔者使用了requests第三方库来执行，关于爬虫可以参考我之前的文章

i. 先把post中的headers格式化

# set the headers or the website will not return information

    # the cookies in here you may need to change

    headers = {

        "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=030393eb0776d20d0975f99b523a70d4; x-requested-with=; "

                  "PHPSESSUD=islilfjn5alth33j9j8glj9776; _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"}

其中cookie部分可能要改，然后最好以你们浏览器上的为主，具体每个参数的含义不是本文范围，可以自行去搜索引擎搜

ii.然后把参数也格式化

# set the parameter, we can get from chrome

    kv = {"sf_url": url,

          "sf_submit": "",

          "new": "1",

          "lang": "en",

          "app": "",

          "country": "cn",

          "os": "Windows",

          "browser": "Chrome"}

其中sf_url字段是我们要下载的youtube视频的url，其他参数都不变

iii. 最后再执行requests库的post请求

# do the POST request

    r = requests.post(url="https://en.savefrom.net/savefrom.php", headers=headers,

                      data=kv)

    r.raise_for_status()

注意是data=kv

iv. 封装成一个函数

import requests

def gethtml(url):

    # set the headers or the website will not return information

    # the cookies in here you may need to change

    headers = {

        "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=030393eb0776d20d0975f99b523a70d4; x-requested-with=; "

                  "PHPSESSUD=islilfjn5alth33j9j8glj9776; _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"}

    # set the parameter, we can get from chrome

    kv = {"sf_url": url,

          "sf_submit": "",

          "new": "1",

          "lang": "en",

          "app": "",

          "country": "cn",

          "os": "Windows",

          "browser": "Chrome"}

    # do the POST request

    r = requests.post(url="https://en.savefrom.net/savefrom.php", headers=headers,

                      data=kv)

    r.raise_for_status()

    # get the result

    return r.text

2. 调用解密函数

i. 分析

这其中的难点在于在python里执行javascript代码，而晚上的解决方法有PyV8等，本文选用execjs。在思路部分我们可以发现js部分的最后几行是解密函数，所以我们只需要在execjs中先执行一遍全部，然后再单独执行解密函数就好了

ii. 先取出js部分

# target(youtube address) url

    url = "https://www.youtube.com/watch?v=YPvtz1lHRiw"

    # get the target text

    reo = gethtml(url)

    # Remove the code from the head and tail (we need the javascript part, information store with encryption in js part)

    reo = reo.split("<script type=\"text/javascript\">")[1].split("</script>")[0]

这里其实可以用正则，不过由于笔者正则表达式还不太熟练就直接用split了

iii. 取第一个解密函数作为我们用的解密函数

当你多取几次不同视频的结果，你就会发现每次的解密函数都不一样，不过位置都是还是在固定行数

# split each line(help us find the decrypt function in last few line)

    reA = reo.split("\n")

    # get the depcrypt function

    name = reA[len(reA) - 3].split(";")[0] + ";"

所以name就是我们的解密函数了(变量名没取太好hhh)

iv. 用execjs执行

# use execjs to execute the js code, and the cwd is the result of `npm root -g`(the path of npm in your computer)

    ct = execjs.compile(reo)

    # do the decryption

    text = ct.eval(name.split("=")[1].replace(";", ""))

其中只取=后面的和去掉分号是指指执行这个函数而不用赋值，当先执行赋值+解密然后取值也不是不可以

但是我们可以发现马上就报错了(要是有这么简单就好了)

1. this也就是window变量不存在

如果没记错是报错this或者$b，笔者尝试把全部this去掉或者把全部框在一个class里面(这样子this就变成那个class了)不过都没有成功，然后发现在npm下有个jsdom可以在execjs里模拟window变量(其实应该有更好方法的)，所以我们需要下载npm和里面的jsdom，然后改写以上代码

    addition = """

    const jsdom = require("jsdom");

    const { JSDOM } = jsdom;

    const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);

    window = dom.window;

    document = window.document;

    XMLHttpRequest = window.XMLHttpRequest;

    """

    # use execjs to execute the js code, and the cwd is the result of `npm root -g`(the path of npm in your computer)

    ct = execjs.compile(addition + reo, cwd=r'C:\Users\xxx\AppData\Roaming\npm\node_modules')

其中

• cwd字段是npm root -g的结果，也就是npm的modules路径
• addition是用来模拟window的
  
  但是我们又可以发现下一个错误

2. alert不存在

这个错误是因为在execjs下执行alert函数是没有意义的，因为我们没有浏览器让他弹窗，且原本alert函数的定义是来源window而我们自定义了window，所以我们要在代码前重写覆盖alert函数(相当于定义一个alert)

# override the alert function, because in the code there has one place using

    # and we cannot do the alerting in execjs(it is meaningless) however, if we donnot override, the code will raise a error

    reo = reo.replace("(function(){", "(function(){\nthis.alert=function(){};")

v. 整合代码

# target(youtube address) url

    url = "https://www.youtube.com/watch?v=YPvtz1lHRiw"

    # get the target text

    reo = gethtml(url)

    # Remove the code from the head and tail (we need the javascript part, information store with encryption in js part)

    reo = reo.split("<script type=\"text/javascript\">")[1].split("</script>")[0]

    # override the alert function, because in the code there has one place using

    # and we cannot do the alerting in execjs(it is meaningless) however, if we donnot override, the code will raise a error

    reo = reo.replace("(function(){", "(function(){\nthis.alert=function(){};")

    # split each line(help us find the decrypt function in last few line)

    reA = reo.split("\n")

    # get the depcrypt function

    name = reA[len(reA) - 3].split(";")[0] + ";"

    # add jsdom into the execjs because the code will use(maybe there is a solution without jsdom, but i have no idea)

    addition = """

    const jsdom = require("jsdom");

    const { JSDOM } = jsdom;

    const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);

    window = dom.window;

    document = window.document;

    XMLHttpRequest = window.XMLHttpRequest;

    """

    # use execjs to execute the js code, and the cwd is the result of `npm root -g`(the path of npm in your computer)

    ct = execjs.compile(addition + reo, cwd=r'C:\Users\19308\AppData\Roaming\npm\node_modules')

    # do the decryption

    text = ct.eval(name.split("=")[1].replace(";", ""))

3. 分析解密结果

i. 取关键json

运行完上面的部分，解密结果就存在text里了，而我们在思路中可以发现，真正对我们重要的就是存在window.parent.sf.videoResult.show()里的json，所以用正则表达式取这一部分的json

# get the result in json

    result = re.search('show\((.*?)\);;', text, re.I | re.M).group(0).replace("show(", "").replace(");;", "")

ii. 格式化json

python可以格式化json的库有很多，这里笔者用了json库(记得import)

# use `json` to load json

    j = json.loads(result)

iii. 取下载地址

接下来就到了最后一步，根据思路里和json格式化工具我们可以发现j["url"][num]["url"]就是下载链接，而num是我们要的视频格式(不同分辨率和类型)

# the selection of video(in this case, num=1 mean the video is

    # - 360p known from j["url"][num]["quality"]

    # - MP4 known from j["url"][num]["type"]

    # - audio known from j["url"][num]["audio"]

    num = 1

    downurl = j["url"][num]["url"]

    # do some download

    # thanks :)

    # - EOF -

3. 全部代码

# -*- coding: utf-8 -*-

# @Time: 2021/1/10

# @Author: Eritque arcus

# @File: Youtube.py

# @License: MIT

# @Environment:

#           - windows 10

#           - python 3.6.2

# @Dependence:

#           - jsdom in npm(windows also can use)

#           - requests, execjs, re, json in python

import requests

import execjs

import re

import json

def gethtml(url):

    # set the headers or the website will not return information

    # the cookies in here you may need to change

    headers = {

        "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=030393eb0776d20d0975f99b523a70d4; x-requested-with=; "

                  "PHPSESSUD=islilfjn5alth33j9j8glj9776; _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"}

    # set the parameter, we can get from chrome

    kv = {"sf_url": url,

          "sf_submit": "",

          "new": "1",

          "lang": "en",

          "app": "",

          "country": "cn",

          "os": "Windows",

          "browser": "Chrome"}

    # do the POST request

    r = requests.post(url="https://en.savefrom.net/savefrom.php", headers=headers,

                      data=kv)

    r.raise_for_status()

    # get the result

    return r.text

if __name__ == '__main__':

    # target(youtube address) url

    url = "https://www.youtube.com/watch?v=YPvtz1lHRiw"

    # get the target text

    reo = gethtml(url)

    # Remove the code from the head and tail (we need the javascript part, information store with encryption in js part)

    reo = reo.split("<script type=\"text/javascript\">")[1].split("</script>")[0]

    # override the alert function, because in the code there has one place using

    # and we cannot do the alerting in execjs(it is meaningless) however, if we donnot override, the code will raise a error

    reo = reo.replace("(function(){", "(function(){\nthis.alert=function(){};")

    # split each line(help us find the decrypt function in last few line)

    reA = reo.split("\n")

    # get the depcrypt function

    name = reA[len(reA) - 3].split(";")[0] + ";"

    # add jsdom into the execjs because the code will use(maybe there is a solution without jsdom, but i have no idea)

    addition = """

    const jsdom = require("jsdom");

    const { JSDOM } = jsdom;

    const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);

    window = dom.window;

    document = window.document;

    XMLHttpRequest = window.XMLHttpRequest;

    """

    # use execjs to execute the js code, and the cwd is the result of `npm root -g`(the path of npm in your computer)

    ct = execjs.compile(addition + reo, cwd=r'C:\Users\19308\AppData\Roaming\npm\node_modules')

    # do the decryption

    text = ct.eval(name.split("=")[1].replace(";", ""))

    # get the result in json

    result = re.search('show\((.*?)\);;', text, re.I | re.M).group(0).replace("show(", "").replace(");;", "")

    # use `json` to load json

    j = json.loads(result)

    # the selection of video(in this case, num=1 mean the video is

    # - 360p known from j["url"][num]["quality"]

    # - MP4 known from j["url"][num]["type"]

    # - audio known from j["url"][num]["audio"]

    num = 1

    downurl = j["url"][num]["url"]

    # do some download

    # thanks :)

    # - EOF -

• 总计102行
• 开发环境

# @Environment:

#           - windows 10

#           - python 3.6.2

• 依赖

# @Dependence:

#           - jsdom in npm(windows also can use)

#           - requests, execjs, re, json in python

-end-

For 爬虫

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本文作者: https://www.cnblogs.com/Eritque-arcus/ 或https://blog.csdn.net/qq_40832960