Keep UVC camera frame rate stable during video calls

tools/chatgui/src/call_video_engine.cpp

@@ -2,6 +2,7 @@
 #include "call_video_encoder.h"
 #include "call_video_decoder.h"
 #include "call_video_cadence.h"
+#include "call_camera_rate.h"
 #include "../../../src/call/call_video_port.h"
 #include "../../../src/call/call_audio.h"
 #include "debug_config.h"
@@ -48,6 +49,7 @@ struct CallVideoEngine::Impl {
     std::unique_ptr<QCamera> camera;
     std::unique_ptr<QMediaCaptureSession> capture;
     std::unique_ptr<QVideoSink> sink;
+    CallCameraRate cameraRate;
     QVideoFrame raw;
 #endif
 };
@@ -105,6 +107,7 @@ void CallVideoEngine::closeCamera() {
 #ifdef HAVE_STREAM_CAPTURE
     if (m->sink) disconnect(m->sink.get(), nullptr, this, nullptr);
     if (m->camera) { disconnect(m->camera.get(), nullptr, this, nullptr); m->camera->stop(); }
+    m->cameraRate.restore();
     m->capture.reset(); m->camera.reset(); m->sink.reset();
     { std::lock_guard<std::mutex> guard(m->lock); m->raw = {}; m->pts = m->backend = m->anchor = -1; }
 #endif
@@ -141,6 +144,10 @@ void CallVideoEngine::setVideo(bool enabled, const QByteArray& cameraId, int wid
     DEBUG_INFO(DEBUG_CATEGORY_CALL, "call camera selected device=%s size=%dx%d pixel=%d fps=%.3f..%.3f",
         selected.id().constData(), selectedFormat.resolution().width(), selectedFormat.resolution().height(),
         selectedFormat.pixelFormat(), selectedFormat.minFrameRate(), selectedFormat.maxFrameRate());
+    connect(m->camera.get(), &QCamera::activeChanged, this, [this, device = selected.id()](bool active) {
+        if (active) m->cameraRate.activate(device);
+        else m->cameraRate.restore();
+    });
     connect(m->sink.get(), &QVideoSink::videoFrameChanged, this, [this, revision](const QVideoFrame& frame) {
         if (!frame.isValid() || !m->running) return;
         std::lock_guard<std::mutex> guard(m->lock);