Wire up graceful degradation and effect preview (FR-7, QF-2, QF-3)

- A failed interpolation or upscaling stage now surfaces a gr.Warning and falls back to
the last successfully-produced result instead of discarding the generated video (QF-2).
- Adds a live "Output: N frames @ X fps, WxHpx" preview that updates as duration, video
fluidity, and upscale settings change, before the user clicks Generate (QF-3).

Closes #7

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app.py

@@ -73,13 +73,21 @@ def run_inference(
         def _report_interpolation_progress(done: int, total: int) -> None:
             progress(0.7 + 0.2 * (done / total), desc=f"Interpolating frames ({done}/{total})...")
 
-        final_frames = interpolate_frames(
-            raw_frames, multiplier=int(frame_factor), progress_callback=_report_interpolation_progress
-        )
+        try:
+            final_frames = interpolate_frames(
+                raw_frames, multiplier=int(frame_factor), progress_callback=_report_interpolation_progress
+            )
+            final_fps = FIXED_FPS * frame_factor
+        except Exception as e:
+            # QF-2: don't discard a successfully generated base video over a post-processing failure.
+            print(f"Interpolation failed, returning base video: {e}")
+            gr.Warning(f"Frame interpolation failed ({e}); returning the video without it.")
+            final_frames = list(raw_frames)
+            final_fps = FIXED_FPS
     else:
         final_frames = list(raw_frames)
+        final_fps = FIXED_FPS
 
-    final_fps = FIXED_FPS * frame_factor
     return final_frames, final_fps
 
 
@@ -123,10 +131,15 @@ def generate_video(
             progress(0.95 + 0.04 * (done / total), desc=f"Upscaling 4x on CPU ({done}/{total} frames)...")
 
         progress(0.95, desc=f"Upscaling 4x on CPU (0/{len(final_frames)} frames)...")
-        pil_frames = [
-            Image.fromarray((np.asarray(frame) * 255.0).round().astype(np.uint8)) for frame in final_frames
-        ]
-        final_frames = upscale_frames(pil_frames, progress_callback=_report_upscale_progress)
+        try:
+            pil_frames = [
+                Image.fromarray((np.asarray(frame) * 255.0).round().astype(np.uint8)) for frame in final_frames
+            ]
+            final_frames = upscale_frames(pil_frames, progress_callback=_report_upscale_progress)
+        except Exception as e:
+            # QF-2: a failed upscale still returns the pre-upscale (interpolated/base) result.
+            print(f"Upscaling failed, returning pre-upscale video: {e}")
+            gr.Warning(f"Upscaling failed ({e}); returning the video without it.")
 
     with tempfile.NamedTemporaryFile(suffix=".mp4", delete=False) as tmpfile:
         video_path = tmpfile.name
@@ -135,6 +148,25 @@ def generate_video(
     return video_path, video_path, current_seed
 
 
+def preview_effect(input_image, duration_seconds, frame_multiplier, upscale_output):
+    """QF-3: show the resulting fps/resolution/duration before the user hits Generate."""
+    num_frames = get_num_frames(duration_seconds)
+    frame_factor = frame_multiplier // FIXED_FPS
+    out_fps = FIXED_FPS * frame_factor if frame_factor > 1 else FIXED_FPS
+    out_frame_count = ((num_frames - 1) * frame_factor + 1) if frame_factor > 1 else num_frames
+
+    if input_image is not None:
+        w, h = resize_image(input_image).size
+    else:
+        w = h = None
+
+    if upscale_output and w is not None:
+        w, h = w * 4, h * 4
+
+    resolution = f"{w}×{h}px" if w is not None else "resolution depends on the uploaded image"
+    return f"**Output:** ~{out_frame_count} frames @ {out_fps} fps, {resolution}"
+
+
 with gr.Blocks() as demo:
     gr.Markdown("# High Quality Video Generation")
     gr.Markdown("Turn a still image into a short video clip guided by a text prompt.")
@@ -164,6 +196,7 @@ with gr.Blocks() as demo:
                 guidance_scale_input = gr.Slider(minimum=0.0, maximum=10.0, step=0.5, value=1.0, label="Guidance Scale")
                 seed_input = gr.Slider(label="Seed", minimum=0, maximum=MAX_SEED, step=1, value=42)
                 randomize_seed_checkbox = gr.Checkbox(label="Randomize seed", value=True)
+            effect_preview = gr.Markdown()
             generate_button = gr.Button("Generate Video", variant="primary")
         with gr.Column():
             video_output = gr.Video(label="Generated Video", autoplay=True)
@@ -186,5 +219,10 @@ with gr.Blocks() as demo:
         outputs=[video_output, file_output, seed_input],
     )
 
+    preview_inputs = [input_image_component, duration_input, frame_multiplier_input, upscale_checkbox]
+    for component in preview_inputs:
+        component.change(fn=preview_effect, inputs=preview_inputs, outputs=effect_preview)
+    demo.load(fn=preview_effect, inputs=preview_inputs, outputs=effect_preview)
+
 if __name__ == "__main__":
     demo.queue().launch(show_error=True)