YouTube Subtitle Translator and Downloader

This project provides a web application and API for fetching, translating, and downloading subtitles (closed captions) from YouTube videos. It leverages the youtube-caption-extractor library for subtitle retrieval and Google's Gemini AI models for high-quality translation.

Features

• Subtitle Extraction: Fetches subtitles directly from YouTube videos using the youtube-caption-extractor library.
• Automatic Language Detection and Dropdown: The application automatically detects all available subtitle languages (including auto-generated ones) for a given YouTube video and presents them in a dropdown menu for the user to select.
• SRT Conversion: The extracted subtitle data is converted into the standard SRT format.
• Translation with Google Gemini AI: Uses Google's Gemini AI models (you'll need your own API key) to translate the subtitles into a target language. The translation process prioritizes natural, conversational tone, and grammatical correctness.
• Progress Updates: The translation process provides progress updates to the user interface. This is especially useful for long videos.
• SRT File Download: Provides the translated (or original) subtitles in the standard SRT (SubRip) format, ready for use with video players.
• Download-Only Mode: Allows users to download the original subtitles (in SRT format) without translation.
• Configurable Translation Batch Size: Lets you control the number of subtitle lines processed per translation request to the Gemini API. This helps manage API usage and avoid rate limits.
• Multiple Gemini Model Support: Allows users to select from a range of Gemini models, balancing speed and quality.
• Clear Error Handling: Provides informative error messages to the user if something goes wrong (e.g., invalid YouTube URL, subtitles disabled, Gemini API key error).
• Simple Web Interface: Includes a user-friendly web interface built with HTML, CSS, and JavaScript. The interface includes a two-step process: 1) Get Video Details (to populate the language dropdown) and 2) Get Subtitles (to fetch the subtitles in the selected language).

How it Works

1. User Input: The user provides a YouTube video URL.
2. Video Details Retrieval: The user clicks "Get Video Details". The application fetches information about the video, including the available subtitle languages. This information is used to populate a dropdown menu of available source languages.
3. Subtitle Language Selection: The user selects the desired source language from the dropdown menu.
4. Subtitle Fetching: The user clicks "Get Subtitles". The application uses youtube-caption-extractor and the selected language code to fetch the appropriate subtitle track from YouTube.
5. SRT Conversion: The fetched subtitle data is converted into the standard SRT format.
6. (Optional) Translation:
   • If the user has provided a Gemini API key and requested translation:
     • The SRT subtitles are split into batches.
     • Each batch is sent to the Google Gemini API for translation.
     • The translated subtitles are used to create the final SRT
     • Progress updates are provided to the user.
7. Download: The final SRT file (either translated or the original) is made available for download.

Project Structure

• server.js: The main Node.js server file. Contains all the server-side logic.
• public/:
  • index.html: The main HTML file, including inline CSS and JavaScript for simplicity.
• package.json: Lists dependencies and scripts.

Setup and Installation

1. Prerequisites:

   • Node.js and npm: (Node.js 12+ recommended) https://nodejs.org/
   • Google Gemini API Key: (If you want to use translation) https://ai.google.dev/

2. Clone/Create Files:

   • Clone: git clone <repository_url> ; cd <project_directory> (If you have a repository)
   • Create: Create the project directory and files (server.js, public/index.html).

3. Install Dependencies:

   npm install express @google/generative-ai youtube-caption-extractor node-fetch uuid

4. Place the Code:

   • Copy the JavaScript code into server.js.
   • Copy the HTML/CSS/JavaScript code into public/index.html.

5. Run the Server:

   node server.js

6. Access the Web Interface: Open http://localhost:3000 in your browser.

API Endpoints

• /get-video-details (POST): Fetches the available subtitle languages for a given YouTube video.

  • Request Body:

    {
        "url": "YOUR_YOUTUBE_VIDEO_URL"
    }

  • Response (Success):

    {
        "availableLanguages": [
            { "code": "en", "name": "English", "isAutoGenerated": false },
            { "code": "fr", "name": "French", "isAutoGenerated": false },
            ...
        ]
    }

  • Response (Error):

    { "error": "Error message" }

    Possible error messages: "YouTube URL is required", "Invalid YouTube URL", or a message indicating a failure to fetch languages.

• /fetch-subtitles (POST): Fetches the subtitles in SRT format.

  • Request Body:

    {
        "url": "YOUR_YOUTUBE_VIDEO_URL",
        "languageCode": "en" // Selected language code (e.g., "en", "fr")
    }

  • Response (Success):

    {
        "srt": "1\n00:00:00,000 --> 00:00:05,000\nSubtitle text...\n\n..."
    }

  • Response (Error):

     { "error": "Error message" }

    Possible error messages include: "YouTube URL is required", "Language code is required", "Invalid YouTube URL", "No subtitles found for language: ...".

• /progress/:id (GET): Get the progress of a translation.

  • Path Parameter:
    • id: The translation ID.
  • Response (Success)

   {
      "message": "Translating lines 1 to 20 of 100",
      "progress": 20,
      "total": 100,
      "completed": false,
      "srt": null
   }

  • Response (Error): json { "error": "Translation not found" }

• /process-subtitles (POST): Translates the subtitles.

  • Request Body:

     {
         "apiKey": "YOUR_GEMINI_API_KEY",
         "srt": "1\n00:00:00,000 --> 00:00:05,000\nSubtitle text...\n\n...",
         "lang": "es", // Target language code (e.g., "es" for Spanish)
         "downloadOnly": false,  // Set to true to skip translation
         "linesPerRequest": 20,  // Number of lines to send per Gemini request
         "model": "gemini-pro" // Gemini model to use
     }

  • Response (Success):

    { "translationId": "UNIQUE_TRANSLATION_ID" }

  • Response (Error):

     { "error": "Error message" }

Troubleshooting

• Gemini API Errors: Check your API key and rate limits. Ensure your key is valid and that you haven't exceeded your quota.
• Subtitles Not Found: Make sure the video has subtitles in the selected language.
• fetch is not a function Error: Make sure you've followed the installation instructions, including installing node-fetch. If you're on an older Node.js, you may need to use dynamic imports (see the code).
• General Errors: Check the server console for detailed error messages.

Contributing

Contributions are welcome! Open an issue or submit a pull request.

License

MIT License