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/routers/download.py

@@ -0,0 +1,62 @@
+from fastapi import APIRouter, BackgroundTasks, HTTPException
+from app.models.schemas import DownloadRequest, DownloadResponse, JobStatus
+from app.models.job_store import job_store
+from app.services.downloader import download_video, detect_platform
+
+router = APIRouter()
+
+
+async def download_task(job_id: str, url: str):
+    """Background task for downloading video."""
+    job_store.update_job(job_id, status=JobStatus.DOWNLOADING, progress=10)
+
+    success, message, video_path = await download_video(url, job_id)
+
+    if success:
+        job_store.update_job(
+            job_id,
+            status=JobStatus.READY_FOR_TRIM,  # Ready for trimming step
+            video_path=video_path,
+            progress=30,
+        )
+    else:
+        job_store.update_job(
+            job_id,
+            status=JobStatus.FAILED,
+            error=message,
+        )
+
+
+@router.post("/", response_model=DownloadResponse)
+async def start_download(
+    request: DownloadRequest,
+    background_tasks: BackgroundTasks
+):
+    """Start video download from URL."""
+    platform = request.platform or detect_platform(request.url)
+
+    # Create job
+    job = job_store.create_job(original_url=request.url)
+
+    # Start background download
+    background_tasks.add_task(download_task, job.job_id, request.url)
+
+    return DownloadResponse(
+        job_id=job.job_id,
+        status=JobStatus.PENDING,
+        message=f"Download started for {platform} video"
+    )
+
+
+@router.get("/platforms")
+async def get_supported_platforms():
+    """Get list of supported platforms."""
+    return {
+        "platforms": [
+            {"id": "douyin", "name": "抖音 (Douyin)", "domains": ["douyin.com", "iesdouyin.com"]},
+            {"id": "kuaishou", "name": "快手 (Kuaishou)", "domains": ["kuaishou.com", "gifshow.com"]},
+            {"id": "bilibili", "name": "哔哩哔哩 (Bilibili)", "domains": ["bilibili.com"]},
+            {"id": "tiktok", "name": "TikTok", "domains": ["tiktok.com"]},
+            {"id": "youtube", "name": "YouTube", "domains": ["youtube.com", "youtu.be"]},
+        ]
+    }