Download many YouTube thumbnails in C#

/*
 * Created by SharpDevelop.
 * User: Admin
 * Date: 5/10/2021
 * Time: 8:52 PM
 *
 * This program is an example of how to download all youtube thumbnails.
 * For working program, please visit my website dosaidsoft.com and look under the software category.
 */
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;
using System.Web;
using System.Net;
using System.Text;
using System.IO;

namespace ThumbExtractor
{
    /// <summary>
    /// Description of MainForm.
    /// </summary>
    public partial class MainForm : Form
    {
        public const string STR_FIND_TITLE = "\"title\":\"";
        public WebClient happy;

        public MainForm()
        {
            InitializeComponent();
            happy = new WebClient();
        }
        void BtnSaveClick(object sender, EventArgs e)
        {
            int count = txtThumb.Lines.Length;
            int cur = 0;

            if (txtPath.Text == "")
            {
                MessageBox.Show("You need to browse for a directory or type one in first!", "Select Folder Please", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                return;
            }
            if (!Directory.Exists(txtPath.Text))
            {
                MessageBox.Show("The directory you put in the box does not exist. Please make it first.", "Folder does not exist", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                return;
            }
            if (!txtPath.Text.EndsWith("\\"))
                txtPath.Text += "\\";

            btnSave.Enabled = false;
            prog.Maximum = count;
            prog.Value = 0;
            foreach (string vid in txtThumb.Lines)
            {
                GetThumb(vid);
                cur++;
                btnSave.Text = cur.ToString() + " / " + count.ToString();
                prog.Value = cur;
                Refresh();
            }
            btnSave.Text = "Save Thumbs";
            btnSave.Enabled = true;
        }

        public void GetThumb(string url)
        {
            //another way for later - provides more data: https://www.youtube.com/get_video_info?video_id=
            //but it's much slower

            string api = "https://noembed.com/embed?url=" + url;
            string ytCode;
            if (url.Contains("youtu.be"))
                ytCode = url.Substring(url.LastIndexOf('/') + 1);
            else
                ytCode = GetArgs(url, "v", '?');
            ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
            string result = happy.DownloadString(api);
            int loc = result.IndexOf(STR_FIND_TITLE);
            loc += STR_FIND_TITLE.Length;
            string theTitle = result.Substring(loc, result.IndexOf('"', loc) - loc);
            string toLoad = "https://i.ytimg.com/vi/" + ytCode + "/hqdefault.jpg";
            string fixedFile = txtPath.Text + ScrubFileName(theTitle) + ".jpg";
            happy.DownloadFile(toLoad, fixedFile);
            picPrev.ImageLocation = fixedFile;
            if (File.Exists(picPrev.ImageLocation))
                picPrev.Load();
        }

        public string GetArgs(string args, string key, char query)
        {
            var iqs = args.IndexOf(query);
            return iqs == -1
                ? string.Empty
                : HttpUtility.ParseQueryString(iqs < args.Length - 1
                    ? args.Substring(iqs + 1) : string.Empty)[key];
        }

        public string ScrubFileName(string value)
        {
           StringBuilder sb = new StringBuilder(value);
           foreach (char item in Path.GetInvalidFileNameChars())
           {
              sb.Replace(item.ToString(), "");
           }
           return sb.ToString();
        }
        void BtnHelpClick(object sender, EventArgs e)
        {
            MessageBox.Show("You paste a list of youtube video links in the box. For getting large batches of links, use the firefox add-on called \"copy selected links\". " +
                            "You then select all the videos (if more than about 50, then do it in segments) and copy them. If there are duplicates or erronious ones, then " +
                            "remove them. You can use the tool at https://dedupelist.com to remove the duplicates, but they shouldn't cause an issue. The images will be stored " +
                            "in the directory you select with the browse button and will be named with the title of the video. Save data will save all the videos info like " +
                            "title, date, url, etc. to a file called YouTube.txt located in the same directory. This is intended to be used in conjunction with a good downloader " +
                            "like mediahuman which will get the youtube videos or audio files to go along with this.\n\n(C) 2021 DosaidSoft. V" + Application.ProductVersion, "Help and About", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
        void BtnBrowseClick(object sender, EventArgs e)
        {
            if (fBrowser.ShowDialog() == DialogResult.OK)
            {
                if (!fBrowser.SelectedPath.EndsWith("\\"))
                    txtPath.Text = fBrowser.SelectedPath + "\\";
                else
                    txtPath.Text = fBrowser.SelectedPath;
            }
        }
        void ChkDataCheckedChanged(object sender, EventArgs e)
        {
            MessageBox.Show("Sorry, this feature is not available in this version. If you want it, please contact me on my website dosaidsoft.com. It will make the download process " +
                            "much slower unfortunately.", "Not available", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
    }
}