Update audio processing state: next_index=51

processing_audio_state.json

@@ -51,6 +51,7 @@
     "audio/week05 04 split knee theory.wav": "failed",
     "audio/week05 03 split knee intro.wav": "failed",
     "audio/week05 02 stretch on the other limbs.wav": "failed",
-    "audio/week05 01 stretchy arms.wav": "failed"
+    "audio/week05 01 stretchy arms.wav": "failed",
+    "audio/week04 16 better spine length measurement.wav": "processing"
   }
 }