fix: transcoding issue

Dockerfile

@@ -9,6 +9,7 @@ COPY requirements.txt ./
 RUN apt-get update && apt-get install -y --no-install-recommends \
         libgl1 \
         libglib2.0-0 \
+        ffmpeg \
     && rm -rf /var/lib/apt/lists/* \
     && pip install --no-cache-dir --upgrade pip \
     && pip install --no-cache-dir -r requirements.txt

requirements.txt

@@ -2,7 +2,7 @@ fastapi
 uvicorn
 torch
 transformers
-opencv-python
+opencv-python-headless
 python-multipart
 accelerate
 pillow

utils/video.py

@@ -1,4 +1,8 @@
 import logging
+import os
+import shutil
+import subprocess
+import tempfile
 from typing import List, Tuple
 
 import cv2
@@ -28,24 +32,48 @@ def extract_frames(video_path: str) -> Tuple[List[np.ndarray], float, int, int]:
     return frames, fps, width, height
 
 
+def _transcode_with_ffmpeg(src_path: str, dst_path: str) -> None:
+    cmd = [
+        "ffmpeg",
+        "-y",
+        "-i",
+        src_path,
+        "-c:v",
+        "libx264",
+        "-preset",
+        "veryfast",
+        "-pix_fmt",
+        "yuv420p",
+        "-movflags",
+        "+faststart",
+        dst_path,
+    ]
+    process = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=False)
+    if process.returncode != 0:
+        raise RuntimeError(process.stderr.decode("utf-8", errors="ignore"))
+
+
 def write_video(frames: List[np.ndarray], output_path: str, fps: float, width: int, height: int) -> None:
     if not frames:
         raise ValueError("No frames available for writing.")
-    candidates = ("avc1", "mp4v")
-    writer = None
-    for codec in candidates:
-        fourcc = cv2.VideoWriter_fourcc(*codec)
-        writer = cv2.VideoWriter(output_path, fourcc, fps or 1.0, (width, height))
-        if writer.isOpened():
-            if codec != candidates[0]:
-                logging.warning("Falling back to %s codec for VideoWriter.", codec)
-            break
-        writer.release()
-        writer = None
-    if writer is None or not writer.isOpened():
-        raise ValueError("Failed to open VideoWriter with a supported codec.")
+    temp_fd, temp_path = tempfile.mkstemp(prefix="raw_", suffix=".mp4")
+    os.close(temp_fd)
+    writer = cv2.VideoWriter(temp_path, cv2.VideoWriter_fourcc(*"mp4v"), fps or 1.0, (width, height))
+    if not writer.isOpened():
+        os.remove(temp_path)
+        raise ValueError("Failed to open VideoWriter.")
 
     for frame in frames:
         writer.write(frame)
 
     writer.release()
+    try:
+        _transcode_with_ffmpeg(temp_path, output_path)
+        logging.debug("Transcoded video to H.264 for browser compatibility.")
+        os.remove(temp_path)
+    except FileNotFoundError:
+        logging.warning("ffmpeg not found; serving fallback MP4V output.")
+        shutil.move(temp_path, output_path)
+    except RuntimeError as exc:
+        logging.warning("ffmpeg transcode failed (%s); serving fallback MP4V output.", exc)
+        shutil.move(temp_path, output_path)