Keep UVC camera frame rate stable during video calls

tools/chatgui/src/call_camera_rate.h

@@ -0,0 +1,63 @@
+#pragma once
+#include <QByteArray>
+#include "debug_config.h"
+#ifdef Q_OS_LINUX
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <linux/videodev2.h>
+#include <cerrno>
+#include <cstring>
+#endif
+
+// Qt задаёт 30 fps, но UVC auto-exposure может разрешить камере снижать их до 16–17.
+// Меняем только этот флаг на время захвата; сама автоэкспозиция остаётся включённой.
+class CallCameraRate {
+#ifdef Q_OS_LINUX
+    int fd = -1;
+#endif
+public:
+    ~CallCameraRate() { restore(); }
+    void restore() {
+#ifdef Q_OS_LINUX
+        if (fd < 0) return;
+        v4l2_control control{}; control.id = V4L2_CID_EXPOSURE_AUTO_PRIORITY; control.value = 1;
+        if (ioctl(fd, VIDIOC_S_CTRL, &control) < 0)
+            DEBUG_WARN(DEBUG_CATEGORY_CALL, "call camera dynamic fps restore failed: %s", std::strerror(errno));
+        else DEBUG_INFO(DEBUG_CATEGORY_CALL, "call camera dynamic fps restored=1");
+        ::close(fd); fd = -1;
+#endif
+    }
+    void activate(const QByteArray& device) {
+        restore();
+#ifdef Q_OS_LINUX
+        if (!device.startsWith("/dev/video")) {
+            DEBUG_DEBUG(DEBUG_CATEGORY_CALL, "call camera fps policy unavailable device=%s", device.constData()); return;
+        }
+        int camera = ::open(device.constData(), O_RDWR | O_NONBLOCK | O_CLOEXEC);
+        if (camera < 0) {
+            DEBUG_WARN(DEBUG_CATEGORY_CALL, "call camera fps control open failed device=%s: %s", device.constData(), std::strerror(errno));
+            return;
+        }
+        v4l2_control control{}; control.id = V4L2_CID_EXPOSURE_AUTO_PRIORITY;
+        if (ioctl(camera, VIDIOC_G_CTRL, &control) < 0) {
+            if (errno == EINVAL) DEBUG_DEBUG(DEBUG_CATEGORY_CALL, "call camera dynamic fps control unsupported device=%s", device.constData());
+            else DEBUG_WARN(DEBUG_CATEGORY_CALL, "call camera fps control read failed: %s", std::strerror(errno));
+        } else if (!control.value) {
+            DEBUG_INFO(DEBUG_CATEGORY_CALL, "call camera dynamic fps already disabled device=%s", device.constData());
+        } else {
+            control.value = 0;
+            if (ioctl(camera, VIDIOC_S_CTRL, &control) < 0)
+                DEBUG_WARN(DEBUG_CATEGORY_CALL, "call camera dynamic fps disable failed: %s", std::strerror(errno));
+            else {
+                fd = camera;
+                DEBUG_INFO(DEBUG_CATEGORY_CALL, "call camera dynamic fps disabled device=%s; auto exposure retained", device.constData());
+                return;
+            }
+        }
+        ::close(camera);
+#else
+        Q_UNUSED(device);
+#endif
+    }
+};

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);