Improve support for changing cam clock frequency

esp32-cam-webserver.ino

@@ -133,6 +133,13 @@ unsigned long imagesServed = 0;  // Total image requests
 // This will be displayed to identify the firmware
 char myVer[] PROGMEM = __DATE__ " @ " __TIME__;
 
+// Camera module bus communications frequency.
+// Originally: config.xclk_freq_hz = 20000000, but this lead to visual artifacts on many modules.
+// See https://github.com/espressif/esp32-camera/issues/150#issuecomment-726473652 et al.
+#if !defined (XCLK_FREQ_HZ)
+    #define XCLK_FREQ_HZ 16500000;
+#endif
+
 // initial rotation
 // can be set in myconfig.h
 #if !defined(CAM_ROTATION)
@@ -482,8 +489,7 @@ void setup() {
     config.pin_sscb_scl = SIOC_GPIO_NUM;
     config.pin_pwdn = PWDN_GPIO_NUM;
     config.pin_reset = RESET_GPIO_NUM;
-    // originally: config.xclk_freq_hz = 20000000;
-    config.xclk_freq_hz = 16500000; // See https://github.com/espressif/esp32-camera/issues/150#issuecomment-726473652 et al.
+    config.xclk_freq_hz = XCLK_FREQ_HZ;
     config.pixel_format = PIXFORMAT_JPEG;
     // Pre-allocate large buffers
     if(psramFound()){

myconfig.sample.h

@@ -179,3 +179,8 @@ struct station stationList[] = {{"ssid1", "pass1", true},
 // #define CAMERA_MODEL_M5STACK_WIDE
 // #define CAMERA_MODEL_M5STACK_ESP32CAM   // Originally: CAMERA_MODEL_M5STACK_NO_PSRAM
 // #define CAMERA_MODEL_TTGO_T_JOURNAL
+
+// Camera module bus communications frequency, setting too high can cause visual artifacts.
+// Currently defaults to 16.5MHz, but some (non-clone) modules may be able to use the 
+// original frequency of 20MHz for to allow higher framerates etc.
+// #define XCLK_FREQ_HZ 20000000;

src/version.h

@@ -1,4 +1,4 @@
 /* Version of upstream code */
 
-char baseVersion[] = "4.0.alpha";
+char baseVersion[] = "4.0.beta2";