Add logging + imageio fallback for API render

app.py

@@ -3402,7 +3402,7 @@ def process_video_api(
         
         # Step 8: Render the final video
         log_msg(f"Rendering video (remove_background={remove_background})")
-        result_video_path = _render_video(api_state, remove_background)
+        result_video_path = _render_video(api_state, remove_background, log_fn=log_msg)
         
         log_msg("Processing complete 🎉")
         return preview_img, result_video_path, "\n".join(log_entries)
@@ -4732,7 +4732,7 @@ with gr.Blocks(title="SAM2 Video (Transformers) - Interactive Segmentation", the
     # Playback via MP4 rendering only
 
     # Render a smooth MP4 using imageio/pyav (fallbacks to imageio v2 / OpenCV)
-    def _render_video(s: AppState, remove_bg: bool = False):
+    def _render_video(s: AppState, remove_bg: bool = False, log_fn=None):
         if s is None or s.num_frames == 0:
             raise gr.Error("Load a video first.")
         fps = s.video_fps if s.video_fps and s.video_fps > 0 else 12
@@ -4756,6 +4756,7 @@ with gr.Blocks(title="SAM2 Video (Transformers) - Interactive Segmentation", the
         frames_np = []
         first = compose_frame(s, start_idx, remove_bg=remove_bg)
         h, w = first.size[1], first.size[0]
+        total_frames = max(1, end_idx - start_idx)
         for idx in range(start_idx, end_idx):
             # Don't use cache when remove_bg changes behavior
             if remove_bg:
@@ -4769,18 +4770,39 @@ with gr.Blocks(title="SAM2 Video (Transformers) - Interactive Segmentation", the
             # Periodically release CPU mem to reduce pressure
             if (idx + 1) % 60 == 0:
                 gc.collect()
-        out_path = "/tmp/sam2_playback.mp4"
-        # Prefer imageio with PyAV/ffmpeg to respect exact fps
-        try:
+            processed = idx - start_idx + 1
+            if log_fn and (processed % 20 == 0 or processed == total_frames):
+                log_fn(f"Rendering frames {processed}/{total_frames}")
+        import tempfile
+        out_file = tempfile.NamedTemporaryFile(delete=False, suffix=".mp4")
+        out_path = out_file.name
+        out_file.close()
+        def _write_with_opencv():
             fourcc = cv2.VideoWriter_fourcc(*"mp4v")
             writer = cv2.VideoWriter(out_path, fourcc, fps, (w, h))
+            if not writer.isOpened():
+                writer.release()
+                raise RuntimeError("OpenCV VideoWriter failed to open (missing codec?).")
             for fr_bgr in frames_np:
                 writer.write(fr_bgr)
             writer.release()
-            return out_path
-        except Exception as e:
-            print(f"Failed to render video with cv2: {e}")
-            raise gr.Error(f"Failed to render video: {e}")
+        def _write_with_imageio():
+            import imageio
+            with imageio.get_writer(out_path, fps=fps, codec="libx264", mode="I", quality=8) as writer:
+                for fr_bgr in frames_np:
+                    writer.append_data(fr_bgr[:, :, ::-1])  # convert back to RGB
+        try:
+            _write_with_opencv()
+        except Exception as cv_err:
+            print(f"OpenCV writer failed: {cv_err}")
+            try:
+                if log_fn:
+                    log_fn("OpenCV writer unavailable, falling back to imageio/pyav.")
+                _write_with_imageio()
+            except Exception as io_err:
+                print(f"Failed to render video: {io_err}")
+                raise gr.Error(f"Failed to render video: {io_err}")
+        return out_path
 
     render_btn.click(_render_video, inputs=[GLOBAL_STATE, remove_bg_checkbox], outputs=[playback_video])