fix: add video download link to waveform panel so it always reflects latest regen

Gradio's built-in gr.Video download button is tied to Svelte state and stays
pointing at the originally generated file even after regen. Added a dedicated
Video download link inside _build_waveform_html (served via /gradio_api/file=)
alongside the existing audio download link. Since the waveform HTML is rebuilt
with the fresh video_path on every regen, this link always downloads the most
recent muxed video. Renamed the existing download button label to Audio for
clarity.

app.py

@@ -841,7 +841,8 @@ def _splice_and_save(new_wav, seg_idx, meta, slot_id):
     state_json_new = json.dumps(_serialised_meta)
 
     waveform_html = _build_waveform_html(audio_path, segments, slot_id, "",
-                                         state_json=state_json_new)
+                                         state_json=state_json_new,
+                                         video_path=video_path)
     return video_path, audio_path, updated_meta, waveform_html
 
 
@@ -1168,7 +1169,7 @@ def _build_regen_pending_html(segments: list, regen_seg_idx: int, slot_id: str,
 
 def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
                          hidden_input_id: str, state_json: str = "",
-                         fn_index: int = -1) -> str:
+                         fn_index: int = -1, video_path: str = "") -> str:
     """Return a self-contained HTML block with a Canvas waveform (display only),
     segment boundary markers, and a download link.
 
@@ -1417,7 +1418,11 @@ def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
     <a href="{data_uri}" download="audio_{slot_id}.wav"
        style="margin-left:auto;background:#333;color:#eee;border:1px solid #555;
               border-radius:4px;padding:3px 10px;font-size:12px;text-decoration:none;">
-      &#8595; Download</a>
+      &#8595; Audio</a>{f'''
+    <a href="/gradio_api/file={video_path}" download="video_{slot_id}.mp4"
+       style="background:#333;color:#eee;border:1px solid #555;
+              border-radius:4px;padding:3px 10px;font-size:12px;text-decoration:none;">
+      &#8595; Video</a>''' if video_path else ''}
   </div>
   <div id="wf_seglabel_{slot_id}"
        style="color:#aaa;font-size:11px;margin-top:4px;min-height:16px;"></div>
@@ -1471,7 +1476,8 @@ def _unpack_outputs(flat: list, n: int, tab_prefix: str) -> list:
             slot_id      = f"{tab_prefix}_{i}"
             state_json   = json.dumps(meta)
             html = _build_waveform_html(aud_path, meta["segments"], slot_id,
-                                        "", state_json=state_json)
+                                        "", state_json=state_json,
+                                        video_path=meta.get("video_path", ""))
             wave_updates.append(gr.update(value=html))
         else:
             wave_updates.append(gr.update(