.

app.py

@@ -1149,6 +1149,7 @@ def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
     window["_wf_video_unlisten_{slot_id}"] = null;
   }}
 
+  console.log('[waveform {slot_id}] script executing');
   const segments  = {segs_json};
   const segColors = {json.dumps(seg_colors)};
   let   audioDuration = 0;
@@ -1207,15 +1208,18 @@ def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
   function drawWaveform(channelData, duration) {{
     audioDuration = duration;
     const canvas  = document.getElementById('wf_canvas_{slot_id}');
-    if (!canvas) return;
+    if (!canvas) {{ console.error('[waveform {slot_id}] drawWaveform: canvas element missing'); return; }}
     const dpr = window.devicePixelRatio || 1;
-    const W   = canvas.getBoundingClientRect().width
+    const rect = canvas.getBoundingClientRect();
+    const W   = rect.width
              || (canvas.parentElement ? canvas.parentElement.getBoundingClientRect().width : 0)
              || 600;
     const H   = 80;
+    console.log('[waveform {slot_id}] drawWaveform W=' + W + ' H=' + H + ' dpr=' + dpr + ' rect=' + JSON.stringify(rect));
     canvas.width  = W * dpr;
     canvas.height = H * dpr;
     const ctx = canvas.getContext('2d');
+    if (!ctx) {{ console.error('[waveform {slot_id}] drawWaveform: could not get 2d context'); return; }}
     ctx.scale(dpr, dpr);
 
     // Background
@@ -1324,9 +1328,11 @@ def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
   // Decode audio immediately (doesn't need canvas dimensions).
   // Drawing is deferred until the canvas actually has a non-zero width.
   const b64str = '{b64}';
+  console.log('[waveform {slot_id}] b64 length=' + b64str.length);
   const bin = atob(b64str);
   const buf = new Uint8Array(bin.length);
   for (let i = 0; i < bin.length; i++) buf[i] = bin.charCodeAt(i);
+  console.log('[waveform {slot_id}] decoded buf size=' + buf.byteLength + ' bytes');
 
   // OfflineAudioContext for decoding — works without user gesture, no playback
   const OfflineCtx = window.OfflineAudioContext || window.webkitOfflineAudioContext;
@@ -1358,14 +1364,14 @@ def _build_waveform_html(audio_path: str, segments: list, slot_id: str,
       tryDraw();
     }};
 
-    // decodeAudioData with promise fallback
-    const decodePromise = tmpCtx.decodeAudioData(buf.buffer.slice(0), doRender, function(err) {{
-      console.error('[waveform {slot_id}] decodeAudioData error:', err);
-    }});
-    if (decodePromise && typeof decodePromise.then === 'function') {{
-      decodePromise.then(doRender).catch(function(err) {{
-        console.error('[waveform {slot_id}] decodeAudioData promise error:', err);
+    // decodeAudioData — use callback form only to avoid double-calling doRender
+    console.log('[waveform {slot_id}] calling decodeAudioData, buf byteLength=' + buf.buffer.byteLength);
+    try {{
+      tmpCtx.decodeAudioData(buf.buffer.slice(0), doRender, function(err) {{
+        console.error('[waveform {slot_id}] decodeAudioData error:', err);
       }});
+    }} catch(e) {{
+      console.error('[waveform {slot_id}] decodeAudioData threw:', e);
     }}
   }}
 }})();