Downloads youtube videos and converts them to mp3 via streaming. ChatpGPT 4 wrote most of this (with minor babysitting from me).

YoutubeDownloader.cs

using NAudio.Wave;
using NAudio.Lame;
using YoutubeExplode;
using YoutubeExplode.Videos.Streams;

namespace YoutubeDownloader
{
    class Program
    {
        static async Task Main(string[] args)
        {
            // Check for the correct number of command-line arguments
            if (args.Length != 2)
            {
                Console.WriteLine("Usage: YoutubeDownloader <url_list_file> <output_dir>");
                return;
            }

            // Parse the command-line arguments
            var urlListFile = args[0];
            var outputDir = args[1];

            // Read the list of URLs from the specified file
            var urls = File.ReadAllLines(urlListFile).Distinct();

            // Create the output directory if it doesn't exist
            Directory.CreateDirectory(outputDir);

            var youtube = new YoutubeClient();

            // Define a function to download and convert a single video
            async Task DownloadVideoAsync(string url)
            {
                try
                {
                    Console.WriteLine($"Getting stream for {url}...");

                    // Get the video information and stream URL
                    var video = await youtube.Videos.GetAsync(url);
                    var outputPath = Path.Combine(outputDir, $"{video.Title}.mp3");

                    Console.WriteLine("Got stream for " + video.Title + " (" + video.Id + ")");

                    if (File.Exists(outputPath))
                    {
                        Console.WriteLine($"Skipping {video.Title} - file already exists");
                        return;
                    }

                    var streamInfoSet = await youtube.Videos.Streams.GetManifestAsync(video.Id);
                    var streamInfo = streamInfoSet.GetAudioOnlyStreams().GetWithHighestBitrate();
                    var streamUrl = streamInfo.Url;

                    Console.WriteLine($"Downloading {video.Title}...");

                    // Download the audio stream and convert it to MP3
                    var inputStream = new MediaFoundationReader(streamUrl);
                    var outputStream = new LameMP3FileWriter(outputPath, inputStream.WaveFormat, LAMEPreset.STANDARD);
                    await inputStream.CopyToAsync(outputStream);

                    Console.WriteLine($"Saved {video.Title} as mp3");
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"Failed to download {url}: {ex.Message}");
                    Console.WriteLine(ex.StackTrace);
                    Console.WriteLine(ex.InnerException);
                }
            }

            // Download the videos with the specified degree of parallelism
            var tasks = urls
                .Select(url =>
                    DownloadVideoAsync(url))
                .AsParallel()
                .WithDegreeOfParallelism(
                    Environment.ProcessorCount);

            await Task.WhenAll(tasks);
        }
    }
}