🎵 Melodiλ - YouTube to Audio Telegram Bot

A Haskell-based Telegram bot for converting YouTube videos to audio tracks.

✨ Features

• 🎧 Download audio from YouTube with best quality
• 🔄 Automatic conversion to MP3 (320kbps)
• 📤 Send tracks directly to Telegram
• 🖼️ Automatic thumbnail extraction from YouTube
• 📝 Video title as audio metadata
• 🔥 Built with Nix for reproducible builds
• ⚡ Asynchronous request processing
• 🛡️ File size limit (50 MB)
• 🔢 Concurrent download control (max 3)
• 🚀 Faster downloads with concurrent fragments

📋 Requirements

• Nix with flakes support
• Telegram account

🚀 Quick Start

1. Install Nix with Flakes

If you don't have Nix installed:

# Install Nix
sh <(curl -L https://nixos.org/nix/install) --daemon

# Enable flakes (add to ~/.config/nix/nix.conf or /etc/nix/nix.conf)
experimental-features = nix-command flakes

2. Create Telegram Bot

1. Open Telegram and find @BotFather
2. Send command /newbot
3. Enter bot name (e.g., Melodilambda Music Bot)
4. Enter bot username (must end with bot, e.g., melodilambda_bot)
5. Get your bot token (looks like 123456789:ABCdefGHIjklMNOpqrsTUVwxyz)

Important: Save the token in a secure place!

3. Clone and Setup

Building for Windows

Option 1: GitHub Actions (Recommended)

The easiest way to get a Windows executable is to use the provided GitHub Actions workflow.

1. Push your code to GitHub.
2. Go to the Actions tab in your repository.
3. Click on the latest Windows Build run.
4. Download the melodilambda-windows-bundle artifact.
5. Extract the archive. It will contain melodilambda.exe, yt-dlp.exe, and ffmpeg.exe ready to go.

Option 2: Nix Cross-Compilation (Experimental)

You can try to cross-compile from Linux using Nix, but this may be unstable due to GHC/MinGW mismatches:

nix build .#windows

Note: For both methods, you will need to download yt-dlp.exe and ffmpeg.exe separately and place them in the same directory as the bot executable.

# Clone the repository
git clone <your-repo-url>
cd Melodiλ

# Create .env file
cp .env.example .env

Edit .env and insert your token:

TELEGRAM_BOT_TOKEN=123456789:ABCdefGHIjklMNOpqrsTUVwxyz

4. Run the Bot

./run.sh

That's it! The script will:

• ✅ Enter Nix development environment
• ✅ Download all dependencies (yt-dlp, ffmpeg, GHC, etc.)
• ✅ Build the project with Stack
• ✅ Run the bot

On any other machine with Nix: Just repeat steps 3-4. Everything is reproducible!

📱 Usage

1. Find your bot in Telegram by username
2. Press /start
3. Send a YouTube video link:

   https://youtu.be/nOJSmXSFCWk
   

4. Wait for conversion
5. Receive the audio file, which you can:
   • Listen directly in Telegram
   • Download to your device
   • Forward to friends

🔧 Development

Development Environment

# Enter Nix development shell
nix develop

# Inside the shell, you have access to:
# - stack (build tool)
# - ghc (Haskell compiler)
# - haskell-language-server (LSP)
# - hlint (linter)
# - ormolu (formatter)
# - yt-dlp & ffmpeg (runtime deps)

# Build
stack --nix build

# Run
stack --nix exec melodilambda

Project Structure

Melodiλ/
├── src/
│   └── Main.hs           # Main bot code
├── downloads/            # Temporary files (auto-created)
├── flake.nix             # Nix flake configuration
├── stack.yaml            # Stack configuration
├── package.yaml          # Haskell dependencies
├── run.sh                # Run script
└── README.md             # Documentation

⚙️ Configuration

Environment Variables

Variable	Description	Required
TELEGRAM_BOT_TOKEN	Bot token from @BotFather	✅

Limits

• Max file size: 50 MB (Telegram limitation)
• Concurrent downloads: 3 simultaneously
• Audio format: MP3
• Audio quality: 0 (best quality, ~320kbps)
• Metadata: Embedded title and thumbnail

Customization

Edit src/Main.hs:

-- Change concurrent download limit (line 73)
if count >= 3  -- Change to desired number

-- Change audio quality (line 147)
"--audio-quality 0"  -- 0 = best, 9 = worst

-- Change format (line 146)
"--audio-format mp3"  -- Options: mp3, m4a, opus, vorbis, wav

-- Disable thumbnail embedding (line 148)
-- "--embed-thumbnail"  -- Comment out this line

-- Disable metadata (line 149)
-- "--add-metadata"  -- Comment out this line

After changes, rebuild:

./run.sh

🐛 Troubleshooting

Bot doesn't respond

1. Check token in .env
2. Verify bot is running (check terminal output)
3. Test with a simple YouTube link

Error: "File too large"

The YouTube video is too long. Try:

• A shorter video

Error: "yt-dlp failed"

1. Check that the link is valid
2. Video might be unavailable or deleted
3. Check your internet connection
4. If the error mentions Failed to resolve / Name or service not known, that's DNS (not yt-dlp): check cat /etc/resolv.conf and getent hosts www.youtube.com in the same environment where the bot runs
5. If you see HTTP Error 403: Forbidden or SABR-related warnings, update yt-dlp (it breaks frequently):
   • Nix: run nix flake update (or update channels) and rebuild
   • Or set MELODILAMBDA_YTDLP=/path/to/yt-dlp to use a newer binary
   • Optional: set MELODILAMBDA_YTDLP_ARGS="--extractor-args youtube:player_client=android" to force a more compatible YouTube client

📚 Tech Stack

• Language: Haskell (GHC 9.4)
• Framework: telegram-bot-simple
• Downloader: yt-dlp
• Converter: ffmpeg
• Build System: Nix + Stack
• Package Manager: Nix

📄 License

MIT License - see LICENSE file for details

🎯 Roadmap

• Playlist support
• Support for other platforms (SoundCloud, Spotify)
• Best audio quality
• Thumbnail extraction
• Video title metadata
• Faster downloads

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Made with ❤️ and λ