AVFoundation: improve changing the capture device format.

Make sure the device format is always set in the same way.
We don't actually set the format anymore when it's the same as
the current one. We also make sure the frame rate is preserved.

Change-Id: I1c68239bc99d9c3cef920effcf47fc253220c26f
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/src/plugins/avfoundation/camera/avfcamerautility.mm b/src/plugins/avfoundation/camera/avfcamerautility.mm
index 712868d22..4bec1dbe9 100644
--- a/src/plugins/avfoundation/camera/avfcamerautility.mm
+++ b/src/plugins/avfoundation/camera/avfcamerautility.mm
@@ -380,6 +380,56 @@ AVFrameRateRange *qt_find_supported_framerate_range(AVCaptureDeviceFormat *forma
     return match;
 }
 
+bool qt_formats_are_equal(AVCaptureDeviceFormat *f1, AVCaptureDeviceFormat *f2)
+{
+    if (f1 == f2)
+        return true;
+
+    if (![f1.mediaType isEqualToString:f2.mediaType])
+        return false;
+
+    return CMFormatDescriptionEqual(f1.formatDescription, f2.formatDescription);
+}
+
+bool qt_set_active_format(AVCaptureDevice *captureDevice, AVCaptureDeviceFormat *format, bool preserveFps)
+{
+    static bool firstSet = true;
+
+    if (!captureDevice || !format)
+        return false;
+
+    if (qt_formats_are_equal(captureDevice.activeFormat, format)) {
+        if (firstSet) {
+            // The capture device format is persistent. The first time we set a format, report that
+            // it changed even if the formats are the same.
+            // This prevents the session from resetting the format to the default value.
+            firstSet = false;
+            return true;
+        }
+        return false;
+    }
+
+    firstSet = false;
+
+    const AVFConfigurationLock lock(captureDevice);
+    if (!lock) {
+        qWarning("Failed to set active format (lock failed)");
+        return false;
+    }
+
+    // Changing the activeFormat resets the frame rate.
+    AVFPSRange fps;
+    if (preserveFps)
+        fps = qt_current_framerates(captureDevice, nil);
+
+    captureDevice.activeFormat = format;
+
+    if (preserveFps)
+        qt_set_framerate_limits(captureDevice, nil, fps.first, fps.second);
+
+    return true;
+}
+
 #endif // SDK
 
 void qt_set_framerate_limits(AVCaptureConnection *videoConnection, qreal minFPS, qreal maxFPS)