streams: add DEBUG logging to SmartCrossFade build and fallback paths

music_assistant/controllers/streams/smart_fades/fades.py

@@ -285,6 +285,17 @@ def _build(self) -> None:
         if is_stretched:
             self._apply_gradual_time_stretch(bpm_ratio, bpm_diff_percent, crossfade_duration)
 
+        self.logger.debug(
+            "SmartCrossFade: out=%.1f BPM, in=%.1f BPM (diff=%.1f%%), bars=%d, "
+            "duration=%.1fs, beat_align=%s, time_stretch=%s",
+            self.fade_out_bpm,
+            self.fade_in_bpm,
+            bpm_diff_percent,
+            crossfade_bars,
+            crossfade_duration,
+            f"{fadein_start_pos:.2f}s" if fadein_start_pos is not None else "none",
+            f"ratio={bpm_ratio:.4f}" if is_stretched else "off",
+        )
         if (
             fadein_start_pos is not None
             and fadein_start_pos + crossfade_duration <= SMART_CROSSFADE_DURATION

music_assistant/controllers/streams/smart_fades/mixer.py

@@ -126,6 +126,25 @@ async def mix(
                     "Smart crossfade failed: %s, falling back to standard crossfade", e
                 )
 
+        # Log why we are falling back to standard crossfade
+        if mode == SmartFadesMode.SMART_CROSSFADE:
+            missing: list[str] = []
+            if not fade_out_analysis:
+                missing.append("no analysis for outgoing track")
+            elif not fade_out_analysis.bpm:
+                missing.append("outgoing BPM unknown")
+            elif fade_out_analysis.beats is None:
+                missing.append("outgoing beats missing")
+            if not fade_in_analysis:
+                missing.append("no analysis for incoming track")
+            elif not fade_in_analysis.bpm:
+                missing.append("incoming BPM unknown")
+            elif fade_in_analysis.beats is None:
+                missing.append("incoming beats missing")
+            self.logger.debug(
+                "Falling back to standard crossfade (%s)",
+                "; ".join(missing) if missing else "unknown reason",
+            )
         # Always fallback to Standard Crossfade in case something goes wrong
         # StandardCrossFade needs full bytes for slicing
         fade_in_bytes = await self._ensure_bytes(fade_in_part)