asyncweb: MJPEG continuous mode

refs #34

Author: yoursunny

examples/AsyncCam/AsyncCam.ino

@@ -34,6 +34,7 @@ setup() {
     Config cfg;
     cfg.setPins(pins::AiThinker);
     cfg.setResolution(initialResolution);
+    cfg.setBufferCount(3);
     cfg.setJpeg(80);
 
     bool ok = Camera.begin(cfg);

examples/AsyncCam/handlers.cpp

@@ -18,9 +18,10 @@ static const char FRONTPAGE[] = R"EOT(
 <input type="submit" value="update">
 </p></form>
 <p id="controls">
-<button data-act="mjpeg">show Motion JPEG stream</button>
-<button data-act="jpg">show still JPEG image</button>
-<button data-act="">hide</button>
+<button data-res="cam.jpg">still JPEG</button>
+<button data-res="cam.mjpeg">MJPEG</button>
+<button data-res="continuous.mjpeg">MJPEG-continuous</button>
+<button data-res="">hide</button>
 </p>
 <div id="display"></div>
 <footer>Powered by <a href="https://esp32cam.yoursunny.dev/">esp32cam</a></footer>
@@ -57,12 +58,8 @@ for (const $ctrl of document.querySelectorAll("#controls button")) {
       $img.src = "";
     }
 
-    const act = evt.target.getAttribute("data-act");
-    if (act === "") {
-      $display.innerHTML = "";
-    } else {
-      $display.innerHTML = `<img src="/cam.${act}?_=${Math.random()}" alt="camera image">`;
-    }
+    const resource = evt.target.getAttribute("data-res");
+    $display.innerHTML = resource && `<img src="/${resource}?_=${Math.random()}" alt="${resource}">`;
   });
 }
 </script>
@@ -172,4 +169,9 @@ addRequestHandlers() {
 
   server.on("/cam.jpg", esp32cam::asyncweb::handleStill);
   server.on("/cam.mjpeg", esp32cam::asyncweb::handleMjpeg);
+  server.on("/continuous.mjpeg", HTTP_GET, [](AsyncWebServerRequest* req) {
+    esp32cam::MjpegConfig cfg;
+    cfg.minInterval = -1;
+    req->send(new esp32cam::asyncweb::MjpegResponse(cfg));
+  });
 }

src/esp32cam/asyncweb.cpp

@@ -11,7 +11,7 @@
 namespace esp32cam {
 namespace detail {
 
-CaptureTask::CaptureTask(uint32_t queueLength, uint32_t priority, int core) {
+CaptureTask::CaptureTask(uint32_t queueLength, uint32_t priority) {
   m_queue = xQueueCreate(queueLength, sizeof(Frame*));
   if (m_queue == nullptr) {
     return;
@@ -41,10 +41,11 @@ CaptureTask::~CaptureTask() {
 }
 
 void
-CaptureTask::request() {
-  if (m_task == nullptr) {
+CaptureTask::request(bool continuous) {
+  if (m_task == nullptr || m_continuous) {
     return;
   }
+  m_continuous = continuous;
   xTaskNotify(reinterpret_cast<TaskHandle_t>(m_task), 1, eSetValueWithOverwrite);
 }
 
@@ -62,10 +63,12 @@ void
 CaptureTask::run(void* ctx) {
   auto self = reinterpret_cast<CaptureTask*>(ctx);
   while (true) {
-    uint32_t value = 0;
-    xTaskNotifyWait(0, UINT32_MAX, &value, pdMS_TO_TICKS(10000));
-    if (value == 0) {
-      continue;
+    if (!self->m_continuous) {
+      uint32_t value = 0;
+      xTaskNotifyWait(0, UINT32_MAX, &value, pdMS_TO_TICKS(10000));
+      if (value == 0) {
+        continue;
+      }
     }
 
     auto frame = Camera.capture().release();
@@ -173,7 +176,7 @@ MjpegResponse::_fillBuffer(uint8_t* buf, size_t buflen) {
       // fallthrough
     }
     case Ctrl::CAPTURE: {
-      m_task.request();
+      m_task.request(m_ctrl.cfg.minInterval < 0);
       m_ctrl.notifyCapture();
       return RESPONSE_TRY_AGAIN;
     }

src/esp32cam/asyncweb.hpp

@@ -10,15 +10,15 @@ namespace detail {
 
 class CaptureTask {
 public:
-  explicit CaptureTask(uint32_t queueLength, uint32_t priority = 1, int core = 1);
+  explicit CaptureTask(uint32_t queueLength, uint32_t priority = 1);
 
   ~CaptureTask();
 
   explicit operator bool() const {
     return m_queue != nullptr && m_task != nullptr;
   }
 
-  void request();
+  void request(bool continuous = false);
 
   std::unique_ptr<Frame> retrieve();
 
@@ -28,6 +28,7 @@ class CaptureTask {
 private:
   void* m_queue = nullptr;
   void* m_task = nullptr;
+  bool m_continuous = false;
 };
 
 } // namespace detail
@@ -81,6 +82,12 @@ handleStill(AsyncWebServerRequest* request) {
  * different images.
  * If task creation fails, respond with HTTP 500 error.
  * If image capture fails, the stream is stopped.
+ *
+ * Normally, a new frame is captured after the prior frame has been fully sent to the client.
+ * Setting MjpegConfig::minInternal to -1 enables continuous mode, in which a new frame is
+ * captured while the prior frame is still being sent to the client. This improves FPS rate
+ * but also increases video latency. This mode is effective only if there are more than one
+ * frame buffer created during camera initialization.
  */
 class MjpegResponse : public AsyncAbstractResponse {
 public:

src/esp32cam/mjpeg.cpp

@@ -25,7 +25,7 @@ MjpegController::decideAction() {
 void
 MjpegController::notifyCapture() {
   m_nextAction = RETURN;
-  m_nextCaptureTime = millis() + static_cast<unsigned long>(cfg.minInterval);
+  m_nextCaptureTime = millis() + static_cast<unsigned long>(std::max(0, cfg.minInterval));
   MC_LOG("notifyCapture next=%lu", m_nextCaptureTime);
 }
 

src/esp32cam/mjpeg.hpp

@@ -11,6 +11,8 @@ namespace esp32cam {
 struct MjpegConfig {
   /**
    * @brief Minimum interval between frame captures in millis.
+   *
+   * Negative value causes @c asyncweb::MjpegResponse to enter continuous mode.
    */
   int minInterval = 0;