Prompt Title: C#: Downloading YouTube Videos.

To download a video from YouTube using C#, you can use a third-party library such as "YoutubeExplode". Here's an example code snippet that demonstrates how to download a video from YouTube using this library:

csharpCopy code
using System.Threading.Tasks;
using YoutubeExplode;
using YoutubeExplode.Models.MediaStreams;

public async Task DownloadYoutubeVideo(string videoUrl, string outputFilePath)
{
    var youtube = new YoutubeClient();

    // Get video information
    var video = await youtube.Videos.GetAsync(videoUrl);

    // Get the best available video stream
    var streamInfo = video.MixedStreams.OrderBy(s => s.VideoQuality).LastOrDefault();

    // Download the video stream to a file
    await youtube.DownloadMediaStreamAsync(streamInfo, outputFilePath);
}

In the above code, you first create an instance of the YoutubeClient class from the YoutubeExplode library. Then, you use this client to retrieve information about the video by calling the GetAsync method on the Videos property.

Next, you retrieve the best available video stream by sorting the video's mixed streams by video quality and selecting the last item in the list. Finally, you download the selected video stream to the specified file path using the DownloadMediaStreamAsync method.

To use this code, you will need to install the YoutubeExplode library using NuGet Package Manager or other methods.

Downloading a video from YouTube without using any external libraries in C# is not a straightforward task because YouTube's servers use a video streaming protocol called DASH (Dynamic Adaptive Streaming over HTTP), which consists of multiple chunks of video and audio data in different resolutions and bitrates. However, you can still achieve this by sending requests to YouTube's servers and parsing the responses manually. Here is a general outline of how you can do it:

1. Send a GET request to the YouTube video URL, including the video ID in the URL. The video ID is the unique identifier for the YouTube video and is usually found in the URL after the "v=" parameter.

2. Parse the HTML response of the GET request to extract the video title, video length, and video streams available. You can use a regular expression or an HTML parsing library like HtmlAgilityPack to extract the relevant information.

3. Select the video stream you want to download based on its resolution and format. The video streams are usually available in MP4 or WEBM formats with different resolutions and bitrates.

4. Send a GET request to the selected video stream URL, including any necessary parameters such as the range of bytes to download.

5. Save the response bytes to a file with the correct file extension.

Here is a sample code snippet that demonstrates how to download a YouTube video without using any external libraries:

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using System.IO;
using System.Net;
using System.Text.RegularExpressions;

public void DownloadYoutubeVideo(string videoUrl, string outputFilePath)
{
    // Extract the video ID from the URL
    var match = Regex.Match(videoUrl, @"v=([\w-]+)");
    var videoId = match.Groups[1].Value;

    // Send a GET request to the YouTube video page
   

To download a video from VK.com (formerly known as VKontakte) using C#, you can use the VK API (Application Programming Interface) to access the video data and download the video file. Here's an example code snippet that demonstrates how to download a video from VK using the VK API:

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using System.IO;
using System.Net;
using Newtonsoft.Json;

public void DownloadVkVideo(string videoUrl, string outputFilePath, string accessToken)
{
    // Extract the video ID from the URL
    var videoId = videoUrl.Substring(videoUrl.LastIndexOf('/') + 1);

    // Send a GET request to the VK API to get video information
    var requestUrl = $"https://api.vk.com/method/video.get?videos={videoId}&access_token={accessToken}&v=5.130";
    var request = WebRequest.Create(requestUrl);
    var response = request.GetResponse();
    var responseStream = response.GetResponseStream();
    var responseReader = new StreamReader(responseStream);
    var responseText = responseReader.ReadToEnd();

    // Parse the JSON response to get the video URL and file name
    dynamic jsonResponse = JsonConvert.DeserializeObject(responseText);
    var videoUrl = jsonResponse.response.items[0].files.mp4_720;
    var fileName = jsonResponse.response.items[0].title + ".mp4";

    // Download the video file using the extracted URL
    using (var client = new WebClient())
    {
        client.DownloadFile(videoUrl, outputFilePath + "\\" + fileName);
    }
}

In the above code, you first extract the video ID from the URL. Then, you send a GET request to the VK API to get information about the video using the video ID and your access token.

Next, you parse the JSON response to get the video URL and file name. In this example, we assume that the video file is available in 720p resolution in the MP4 format. You can change the video URL and file name properties according to your needs.

Finally, you download the video file using the extracted URL and save it to the specified file path using the DownloadFile method of the WebClient class.

Note that to use this code, you will need to obtain an access token from VK.com and provide it as a parameter to the DownloadVkVideo method.