 ColorIntensity r_intensity;
 ColorIntensity g_intensity;
 ColorIntensity b_intensity;
+#define BRIGHTNESS_STEP 32
+
 int8_t speed;
-
-#define BRIGHTNESS_STEP 32
-const int8_t MIN_SPEED = -6;
-const int8_t MAX_SPEED = 4;
+const int8_t MIN_SPEED = -6;     // Playing backward at 5x normal rate
+const int8_t MAX_SPEED = 4;      // Playing forward at 5x normal rate
+
+int8_t frame_len;
+const int8_t MIN_FRAME_LEN = -1; // Each frame lasts 0.5x normal time (25ms shorter)
+const int8_t MAX_FRAME_LEN = 4;  // Each frame lasts 3x normal time (100ms longer)
 
 //------------------------------------------------------------------------------
 // File system object.

       || ops.increase_speed
       || ops.toggle_pause
       || ops.toggle_negative
       || ops.reset_settings)
  {
    printSettings();
  }

  Serial.print(negative);
  Serial.print(F(" speed "));
  Serial.print(speed);
  Serial.print(F(" frame_len "));
  Serial.print(frame_len);
}

void resetDefaultSettings()
