refactor: cap waveform decode length + guard frombuffer + tighten test

core/waveform.py

@@ -32,4 +32,6 @@ def load_region_samples(path: str, start: float, duration: float,
         return np.zeros(0, dtype="float32")
     if proc.returncode != 0 or not proc.stdout:
         return np.zeros(0, dtype="float32")
-    return np.frombuffer(proc.stdout, dtype="float32")
+    buf = proc.stdout
+    buf = buf[: len(buf) - (len(buf) % 4)]
+    return np.frombuffer(buf, dtype="float32")

main.py

@@ -6511,12 +6511,17 @@ class MainWindow(QMainWindow):
         from core.waveform import load_region_samples, peaks
         start = self._cursor
         dur = self._spn_audio_len.value()
+        preview = min(dur, 120.0)   # cap decode; the strip is 128 bars regardless
         QApplication.setOverrideCursor(Qt.CursorShape.WaitCursor)
         try:
-            samples = load_region_samples(self._file_path, start, dur)
+            samples = load_region_samples(self._file_path, start, preview)
         finally:
             QApplication.restoreOverrideCursor()
         self._wave.set_peaks(peaks(samples))
+        if samples.size == 0:
+            self._show_status("Waveform: no audio decoded", 3000)
+        elif preview < dur:
+            self._show_status(f"Waveform shows first {preview:.0f}s of {dur:.0f}s", 4000)
 
     def _on_extract_audio(self) -> None:
         """Extract an exact-length audio slice starting at the playhead and

tests/test_utils.py

@@ -551,6 +551,8 @@ def test_peaks_downsamples_to_bucket_count():
     p = peaks(samples, buckets=64)
     assert len(p) == 64
     assert all(0.0 <= v <= 1.0 for v in p)
+    import pytest
+    assert max(p) == pytest.approx(1.0)
 
 
 def test_peaks_empty_returns_zeros():