API плейлистов YouTube не возвращает все видео на канале

Если сам API не работает, вы можете рассмотреть возможность перемещения по XML, аналогично этому:

internal async Task<VideoInfo[]> GetDataFromWebsite(string url)
{
    //strings used for traversing the website
    string startSearch = "else {window.addEventListener('script-load-dpj',";
    string endSearch = "</div>";
    string beforeEachEntry = "\"ADD_TO_QUEUE_TAIL\"";
    string beforeurl = "{\"webCommandMetadata\":{\"url\":\"/watch";
    string afterUrl = "\",\"webPageType\"";
    string filterTitleBetter = ",\"width\":336,\"height\":188}]}";
    string beforeTitle = ",\"title\":{\"runs\":[{\"text\":\"";
    string aftertitle = "\"";

    VideoInfo[] videoInfos;

    using (HttpClient client = new HttpClient())
    {
        //Get a response from Youtube
        HttpResponseMessage response = await client.GetAsync(url);

        //check if the Request was successful
        if (response.IsSuccessStatusCode)
        {
            //Get the XML from the response
            string xml = await response.Content.ReadAsStringAsync();

            //narrow down the section where we search for useful data
            string[] allData = xml.Split(startSearch)[1].Split(endSearch)[0].Split(beforeEachEntry);

            //initialize the return object 
            //the size is one less than allData.Length because the first entry contains no data
            videoInfos = new VideoInfo[allData.Length - 1];

            //iterate through the data
            for (int i = 1; i < allData.Length; i++)
            {
                //narrow down the entry section for the title
                string[] splitForVideoName = allData[i].Split(filterTitleBetter);
                //split the entry string exactly to contain the video title
                string videoName = splitForVideoName[splitForVideoName.Length - 1].Split(beforeTitle)[1].Split(aftertitle)[0];

                //split the entry string exactly to contain the video url
                string videoURL = "https://www.youtube.com/watch" + allData[i].Split(beforeurl)[1].Split(afterUrl)[0];

                //add those information to our return object
                videoInfos[i - 1] = new VideoInfo() { videoURL = videoURL, videoName = videoName };
            }
            client.Dispose();
            return videoInfos;
        }
        else
        {
            client.Dispose();
            throw new Exception();
        }
    }

internal class VideoInfo
{
    internal string videoURL;
    internal string videoName;
}

Чтобы стать полностью функциональным для каждого плейлиста, потребуется еще немного поработать, но с https://www.youtube.com/playlist?list=PLlVlyGVtvuVlklX5bYqk9RHnOSmUP6j0h до сих пор это работало.

Я исследовал много разных подходов, и единственный, который, кажется, работает идеально, — это следующий, основанный на веб-скрапинге вкладки Videos указанного канала:

import requests
from lxml import html
import json

CHANNEL_HANDLE = '@MLB'
text = requests.get(f'https://www.youtube.com/{CHANNEL_HANDLE}/videos').text
tree = html.fromstring(text)

ytVariableName = 'ytInitialData'
ytVariableDeclaration = ytVariableName + ' = '
for script in tree.xpath('//script'):
    scriptContent = script.text_content()
    if ytVariableDeclaration in scriptContent:
        ytVariableData = json.loads(scriptContent.split(ytVariableDeclaration)[1][:-1])
        break

contents = ytVariableData['contents']['twoColumnBrowseResultsRenderer']['tabs'][1]['tabRenderer']['content']['richGridRenderer']['contents']

videoIds = set()

def treatContents(contents):
    for content in contents:
        if not 'richItemRenderer' in content:
            break
        videoId = content['richItemRenderer']['content']['videoRenderer']['videoId']
        videoIds.add(videoId)
    print(len(videoIds))
    return getContinuationToken(contents)

def getContinuationToken(contents):
    # Sometimes have 29 actual results instead of 30.
    lastContent = contents[-1]
    if not 'continuationItemRenderer' in lastContent:
        return None
    return lastContent['continuationItemRenderer']['continuationEndpoint']['continuationCommand']['token']

continuationToken = treatContents(contents)
if continuationToken is not None:
    url = 'https://www.youtube.com/youtubei/v1/browse'
    headers = {
        'Content-Type': 'application/json'
    }
    requestData = {
        'context': {
            'client': {
                'clientName': 'WEB',
                'clientVersion': '2.20240313.05.00'
            }
        }
    }
    while True:
        requestData['continuation'] = continuationToken
        data = requests.post(url, headers = headers, json = requestData).json()
        # Happens not deterministically sometimes.
        if not 'onResponseReceivedActions' in data:
            print('Retrying')
            continue
        continuationItems = data['onResponseReceivedActions'][0]['appendContinuationItemsAction']['continuationItems']
        continuationToken = treatContents(continuationItems)
        if continuationToken is None:
            break

Хотя @MLBAbout утверждает 291,597 videos, мой метод находит 289,814 уникальные видео. Неизвестно, откуда взялась разница в количестве, возможно, из-за Live и видео, не включенных в список.