如果只是想获取弹幕文件呢，用之前的代码就浪费太多时间了。
所以用B站官方的api做了一点改进。(没有查到除了b站官方api之外的其他方便的下载弹幕的方法)
效果如下:


代码如下：

import requests
import json
from tqdm import tqdm
from bs4 import BeautifulSoup
from xml.dom.minidom import parseString

headers = {
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.54 Safari/537.36"}

def get_resp_text(url):
    rsp = requests.get(url,headers=headers)
    rsp.encoding = 'utf-8'
    return rsp.text
def get_upname(mid):
        global upname
        rsp = requests.get('https://space.bilibili.com/'+mid)
        rsp.encoding = 'utf-8'
        html = rsp.text
        bss = BeautifulSoup(html, 'lxml')
        return (bss.find('title').text[:-len('的个人空间_哔哩哔哩_Bilibili')])
def get_bvid(mid):
    i = 1
    bvid = []
    while i != 0:
        url0 = 'https://api.bilibili.com/x/space/arc/search?mid=' + str(
            mid) + '&ps=30&tid=0&pn=&keyword=&order=pubdate&jsonp=jsonp'
        url0 = url0[:-len('&keyword=&order=pubdate&jsonp=jsonp')] + str(
            i) + '&keyword=&order=pubdate&jsonp=jsonp'
        i += 1
        rsp = requests.get(url0, headers=headers)
        rsp.encoding = 'utf-8'
        html = rsp.text
        dict = json.loads(html.replace('\n', ''))
        datadict = dict['data']
        listdict = datadict['list']
        vlist = listdict['vlist']
        if len(vlist) == 0:
            i = 0
        elif len(vlist) != 0:
            for _ in range(len(vlist)):
                bvid.insert(0, vlist[_]['bvid'])
    print("bv号已经爬取完毕")
    return bvid
def get_cid_url(bvid):
    cid_url = []
    for bid in bvid:
        cid_url.insert(0,'https://api.bilibili.com/x/player/pagelist?bvid=' + str(bid) + '&jsonp=jsonp')
    return cid_url
def get_cids(cid_urls):
    cids = []
    for cid_url in cid_urls:
        str = get_resp_text(cid_url)
        jsonstr = json.loads(str)
        jsrdata = jsonstr['data']
        jsrdict = jsrdata[0]
        cids.insert(0,jsrdict['cid'])
    return cids
def get_xml_url(cids):
    xml_urls = []
    for cid in cids:
        xml_urls.insert(0,'https://api.bilibili.com/x/v1/dm/list.so?oid='+str(cid))
    return xml_urls
def get_xmls(xml_urls):
    xmls = []
    for xml_url in xml_urls:
        xmls.insert(0,get_resp_text(xml_url))
    return xmls
def get_danmus(xmls):
    danmus = []
    for xml in xmls:
        tanmus = parseString(xml).documentElement.getElementsByTagName('d')
        for tanmu in tanmus:
            tanmu = tanmu.childNodes[0].data
            danmus.insert(0, tanmu)
    print("弹幕已经爬取完毕"+'\n正在下载至本地')
    return danmus
def save_danmus(upname,danmus):
    with open(upname+".txt",'w',encoding='utf-8') as f:
        for danmu in  tqdm(danmus):
            f.write(danmu+"\n")
    print("共有弹幕:" + str(len(danmus)) + "条已下载至"+upname+".txt")

if __name__ =='__main__':
    uid = input("请输入up主的uid:")
    upname = get_upname(uid)
    print("你想要查询的up主是" + upname + "吧" + "\n稍等一会儿~~")
    bvid = get_bvid(uid)
    cid_urls = get_cid_url(bvid)
    cids = get_cids(cid_urls)
    xml_urls = get_xml_url(cids)
    xmls = get_xmls(xml_urls)
    danmus = get_danmus(xmls)
    save_danmus(upname, danmus)