Initial commit: YouTube Shorts maker application

Features:
- Video download from TikTok/Douyin using yt-dlp
- Audio transcription with OpenAI Whisper
- GPT-4 translation (direct/summarize/rewrite modes)
- Subtitle generation with ASS format
- Video trimming with frame-accurate preview
- BGM integration with volume control
- Intro text overlay support
- Thumbnail generation with text overlay

Tech stack:
- Backend: FastAPI, Python 3.11+
- Frontend: React, Vite, TailwindCSS
- Video processing: FFmpeg
- AI: OpenAI Whisper, GPT-4

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/downloader.py

@@ -0,0 +1,158 @@
+import subprocess
+import os
+import re
+from typing import Optional, Tuple
+from app.config import settings
+
+
+def detect_platform(url: str) -> str:
+    """Detect video platform from URL."""
+    if "douyin" in url or "iesdouyin" in url:
+        return "douyin"
+    elif "kuaishou" in url or "gifshow" in url:
+        return "kuaishou"
+    elif "bilibili" in url:
+        return "bilibili"
+    elif "youtube" in url or "youtu.be" in url:
+        return "youtube"
+    elif "tiktok" in url:
+        return "tiktok"
+    else:
+        return "unknown"
+
+
+def sanitize_filename(filename: str) -> str:
+    """Sanitize filename to be safe for filesystem."""
+    # Remove or replace invalid characters
+    filename = re.sub(r'[<>:"/\\|?*]', '_', filename)
+    # Limit length
+    if len(filename) > 100:
+        filename = filename[:100]
+    return filename
+
+
+def get_cookies_path(platform: str) -> Optional[str]:
+    """Get cookies file path for a platform."""
+    cookies_dir = os.path.join(os.path.dirname(settings.DOWNLOAD_DIR), "cookies")
+
+    # Check for platform-specific cookies first (e.g., douyin.txt)
+    platform_cookies = os.path.join(cookies_dir, f"{platform}.txt")
+    if os.path.exists(platform_cookies):
+        return platform_cookies
+
+    # Check for generic cookies.txt
+    generic_cookies = os.path.join(cookies_dir, "cookies.txt")
+    if os.path.exists(generic_cookies):
+        return generic_cookies
+
+    return None
+
+
+async def download_video(url: str, job_id: str) -> Tuple[bool, str, Optional[str]]:
+    """
+    Download video using yt-dlp.
+
+    Returns:
+        Tuple of (success, message, video_path)
+    """
+    output_dir = os.path.join(settings.DOWNLOAD_DIR, job_id)
+    os.makedirs(output_dir, exist_ok=True)
+
+    output_template = os.path.join(output_dir, "%(title).50s.%(ext)s")
+
+    # yt-dlp command with options for Chinese platforms
+    cmd = [
+        "yt-dlp",
+        "--no-playlist",
+        "-f", "best[ext=mp4]/best",
+        "--merge-output-format", "mp4",
+        "-o", output_template,
+        "--no-check-certificate",
+        "--socket-timeout", "30",
+        "--retries", "3",
+        "--user-agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36",
+    ]
+
+    platform = detect_platform(url)
+
+    # Add cookies if available (required for Douyin, Kuaishou)
+    cookies_path = get_cookies_path(platform)
+    if cookies_path:
+        cmd.extend(["--cookies", cookies_path])
+        print(f"Using cookies from: {cookies_path}")
+    elif platform in ["douyin", "kuaishou", "bilibili"]:
+        # Try to use browser cookies if no cookies file
+        # Priority: Chrome > Firefox > Edge
+        cmd.extend(["--cookies-from-browser", "chrome"])
+        print(f"Using cookies from Chrome browser for {platform}")
+
+    # Platform-specific options
+    if platform in ["douyin", "kuaishou"]:
+        # Use browser impersonation for anti-bot bypass
+        cmd.extend([
+            "--impersonate", "chrome-123:macos-14",
+            "--extractor-args", "generic:impersonate",
+        ])
+
+    # Add proxy if configured (for geo-restricted platforms)
+    if settings.PROXY_URL:
+        cmd.extend(["--proxy", settings.PROXY_URL])
+        print(f"Using proxy: {settings.PROXY_URL}")
+
+    cmd.append(url)
+
+    try:
+        result = subprocess.run(
+            cmd,
+            capture_output=True,
+            text=True,
+            timeout=300,  # 5 minute timeout
+        )
+
+        if result.returncode != 0:
+            error_msg = result.stderr or result.stdout or "Unknown error"
+            return False, f"Download failed: {error_msg}", None
+
+        # Find the downloaded file
+        for file in os.listdir(output_dir):
+            if file.endswith((".mp4", ".webm", ".mkv")):
+                video_path = os.path.join(output_dir, file)
+                return True, "Download successful", video_path
+
+        return False, "No video file found after download", None
+
+    except subprocess.TimeoutExpired:
+        return False, "Download timed out (5 minutes)", None
+    except Exception as e:
+        return False, f"Download error: {str(e)}", None
+
+
+def get_video_info(url: str) -> Optional[dict]:
+    """Get video metadata without downloading."""
+    cmd = [
+        "yt-dlp",
+        "-j",  # JSON output
+        "--no-download",
+    ]
+
+    # Add proxy if configured
+    if settings.PROXY_URL:
+        cmd.extend(["--proxy", settings.PROXY_URL])
+
+    cmd.append(url)
+
+    try:
+        result = subprocess.run(
+            cmd,
+            capture_output=True,
+            text=True,
+            timeout=60,
+        )
+
+        if result.returncode == 0:
+            import json
+            return json.loads(result.stdout)
+    except Exception:
+        pass
+
+    return None