Hey there! Great question—when dealing with large video files (350MB+) in your Flask-powered Telegram Bot, you can’t rely on naive download methods (like loading the entire file into memory at once). Here’s the right approach using Telegram’s Bot API:

Core Method: getFile + Streamed Download #

The key is to use Telegram’s getFile API endpoint to retrieve a temporary download URL for the file, then perform a streamed, chunked download to your server. This avoids memory overload and timeouts that come with pulling huge files in one go.

Step-by-Step Breakdown #

1. Extract the File ID: When a user sends a video, your Flask webhook will receive an update containing the video object. Grab its file_id from the payload.
2. Fetch File Metadata: Call the getFile API with the file_id to get the file_path (this is the path to the file on Telegram’s servers).
3. Construct Download URL: Build the full download URL using your bot token and the file_path.
4. Stream the Download: Use a library like requests to download the file in small chunks, writing each chunk to disk immediately instead of storing the whole file in memory.

Example Flask Code #

Here’s a minimal working example using Flask and requests:

import requests
from flask import Flask, request

app = Flask(__name__)
BOT_TOKEN = "your_actual_bot_token_here"

@app.route('/telegram-webhook', methods=['POST'])
def handle_webhook():
    update = request.get_json()
    
    # Check if the update contains a video message
    if not update.get('message') or not update['message'].get('video'):
        return 'OK'
    
    video_data = update['message']['video']
    file_id = video_data['file_id']
    chat_id = update['message']['chat']['id']

    # Step 1: Get file details from Telegram API
    get_file_endpoint = f"https://api.telegram.org/bot{BOT_TOKEN}/getFile"
    file_info = requests.get(get_file_endpoint, params={'file_id': file_id}).json()
    
    if not file_info['ok']:
        # Send error message to user
        requests.post(
            f"https://api.telegram.org/bot{BOT_TOKEN}/sendMessage",
            data={'chat_id': chat_id, 'text': "Failed to retrieve video details. Please try again."}
        )
        return 'OK'

    # Step 2: Build the direct download URL
    file_path = file_info['result']['file_path']
    download_url = f"https://api.telegram.org/file/bot{BOT_TOKEN}/{file_path}"

    # Step 3: Stream download the large video
    try:
        with open(f"downloaded_video_{chat_id}.mp4", 'wb') as output_file:
            with requests.get(download_url, stream=True, timeout=300) as response:
                response.raise_for_status()
                # Download in 8KB chunks (adjust size based on your server's memory)
                for chunk in response.iter_content(chunk_size=8192):
                    output_file.write(chunk)
        
        # Notify user of success
        requests.post(
            f"https://api.telegram.org/bot{BOT_TOKEN}/sendMessage",
            data={'chat_id': chat_id, 'text': "Your large video has been downloaded successfully!"}
        )
    except Exception as e:
        # Handle download errors (timeouts, network issues, etc.)
        requests.post(
            f"https://api.telegram.org/bot{BOT_TOKEN}/sendMessage",
            data={'chat_id': chat_id, 'text': f"Download failed: {str(e)}"}
        )

    return 'OK'

if __name__ == '__main__':
    # For production, use a proper WSGI server like Gunicorn instead of Flask's dev server
    app.run(host='0.0.0.0', port=5000, debug=False)

Critical Notes for Large Files #

• Streamed Downloads are Non-Negotiable: Using stream=True and iter_content ensures you don’t load the entire 350MB+ file into RAM, which would crash most servers.
• Timeout Settings: Adjust the timeout parameter in requests.get to account for longer download times (5 minutes is a safe start for large files).
• Production Server: Flask’s built-in development server isn’t designed for heavy traffic or long-running downloads. Use Gunicorn, uWSGI, or a similar WSGI server in production.
• File Expiry: Telegram’s download URLs are only valid for 1 hour, so process the file immediately after retrieving the URL.
• Error Handling: Add robust error catching for network issues, disk space limits, and Telegram API failures—your users will appreciate clear feedback.

内容的提问来源于stack exchange，提问作者Negar