Initial commit: Børnetime app scaffold

FastAPI + Celery + Svelte app for English→Danish video translation
with voice cloning. Includes diarization, STT, translation, TTS,
and audio mixing pipeline.

backend/app/services/video_utils.py

@@ -0,0 +1,47 @@
+import subprocess
+import os
+from typing import Optional
+from ..config import settings
+
+
+def get_video_duration(path: str) -> Optional[float]:
+    cmd = [
+        "ffprobe",
+        "-v",
+        "error",
+        "-show_entries",
+        "format=duration",
+        "-of",
+        "default=noprint_wrappers=1:nokey=1",
+        path,
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True)
+    if result.returncode == 0 and result.stdout.strip():
+        return float(result.stdout.strip())
+    return None
+
+
+def extract_audio(video_path: str, output_path: str, sample_rate: int = 16000) -> str:
+    cmd = [
+        "ffmpeg",
+        "-y",
+        "-i",
+        video_path,
+        "-vn",
+        "-acodec",
+        "pcm_s16le",
+        "-ar",
+        str(sample_rate),
+        "-ac",
+        "1",
+        output_path,
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True)
+    if result.returncode != 0:
+        raise RuntimeError(f"Audio extraction failed: {result.stderr}")
+    return output_path
+
+
+def build_output_path(video_path: str) -> str:
+    base, ext = os.path.splitext(os.path.basename(video_path))
+    return f"{base}_en_da_audio{ext}"