Play file m3u8 in windows form.

M3U[^] is a playlist; it's a plain-text file containing a list of URLs representing the files to play, and optionally comment lines starting with #.

You'll need to read the contents of the file, extract any URLs, and process them accordingly:

IEnumerable<Uri> LoadPlaylist(Uri source)
{
    using (var client = new WebClient())
    {
        var processedPlaylists = new HashSet<Uri>();
        var playlists = new Queue<Uri>();
        playlists.Enqueue(source);
        
        while (playlists.Count != 0)
        {
            Uri playlistUri = playlists.Dequeue();
            if (!processedPlaylists.Add(playlistUri)) continue;
            
            string playlistContent = client.DownloadString(playlistUri);
            string[] playlistLines = playlistContent.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries);
            
            foreach (string line in playlistLines)
            {
                if (string.IsNullOrWhiteSpace(line)) continue;
                if (line[0] == '#') continue;
                
                Uri file;
                if (!Uri.TryCreate(source, line, out file))
                {
                    Console.WriteLine("Invalid line: '{0}'", line);
                    continue;
                }
            
                string extension = Path.GetExtension(file.LocalPath);
                if (extension.StartsWith(".m3u", StringComparison.OrdinalIgnoreCase))
                {
                    playlists.Enqueue(file);
                }
                else
                {
                    yield return file;
                }
            }
        }
    }
}

Running that against the URL in your question produces three .aac files:
Advanced Audio Coding - Wikipedia, the free encyclopedia[^]

If you want to use that playlist, then you'll need to update your module to support that file type.