GStreamer: QGstreamerVideoSink - add capsfilter for pixel-aspect-ratio

By adding a caps filter to the videoSinkBin and using a
videoconvertscale instead of a videoconvert element, we can obtain a
square pixel scaling on the application-side

Task-number: QTBUG-108754
Pick-to: 6.6 6.5
Change-Id: I9fb95ad1075b34b4dd3dec9bee8b1c254e924a19
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Mikko Hallamaa <mikko.hallamaa@qt.io>
Reviewed-by: Lars Sutterud <lars.sutterud@qt.io>
(cherry picked from commit e7b801361654eedbb844865ef5b4454492ee2323)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 27 insertions, 6 deletions

diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
index f5318d79a..3825e7f20 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
@@ -15,9 +15,9 @@ QT_BEGIN_NAMESPACE
 
 QMaybe<QGstreamerVideoOutput *> QGstreamerVideoOutput::create(QObject *parent)
 {
-    QGstElement videoConvert = QGstElement::createFromFactory("videoconvert", "videoConvert");
+    QGstElement videoConvert = QGstElement::createFromFactory("videoconvertscale", "videoConvert");
     if (!videoConvert)
-        return errorMessageCannotFindElement("videoconvert");
+        return errorMessageCannotFindElement("videoconvertscale");
 
     QGstElement videoSink = QGstElement::createFromFactory("fakesink", "fakeVideoSink");
     if (!videoSink)
diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
index 73276bae5..4af96b37d 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
@@ -68,8 +68,28 @@ QGstreamerVideoSink::QGstreamerVideoSink(QVideoSink *parent)
         QGstElement::NeedsRef,
     };
 
-    sinkBin.add(gstQueue, gstPreprocess);
-    qLinkGstElements(gstQueue, gstPreprocess);
+    bool disablePixelAspectRatio =
+            qEnvironmentVariableIsSet("QT_MULTIMEDIA_GSTREAMER_DISABLE_PIXEL_ASPECT_RATIO");
+    if (disablePixelAspectRatio) {
+        // Enabling the pixel aspect ratio may expose a gstreamer bug on cameras that don't expose a
+        // pixel-aspect-ratio via `VIDIOC_CROPCAP`. This can cause the caps negotiation to fail.
+        // Using the QT_MULTIMEDIA_GSTREAMER_DISABLE_PIXEL_ASPECT_RATIO environment variable, on can
+        // disable pixel-aspect-ratio handling
+        //
+        // compare: https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6242
+        gstCapsFilter =
+                QGstElement::createFromFactory("identity", "nullPixelAspectRatioCapsFilter");
+    } else {
+        gstCapsFilter = QGstElement::createFromFactory("capsfilter", "pixelAspectRatioCapsFilter");
+        QGstCaps capsFilterCaps{
+            gst_caps_new_simple("video/x-raw", "pixel-aspect-ratio", GST_TYPE_FRACTION, 1, 1, NULL),
+            QGstCaps::HasRef,
+        };
+        g_object_set(gstCapsFilter.element(), "caps", capsFilterCaps.release(), NULL);
+    }
+
+    sinkBin.add(gstQueue, gstPreprocess, gstCapsFilter);
+    qLinkGstElements(gstQueue, gstPreprocess, gstCapsFilter);
     sinkBin.addGhostPad(gstQueue, "sink");
 
     gstSubtitleSink = QGstElement(GST_ELEMENT(QGstSubtitleSink::createSink(this)));
@@ -141,8 +161,8 @@ void QGstreamerVideoSink::updateSinkElement()
 
     gstVideoSink = newSink;
     sinkBin.add(gstVideoSink);
-    if (!qLinkGstElements(gstPreprocess, gstVideoSink))
-        qCDebug(qLcMediaVideoSink) << "couldn't link preprocess and sink";
+    if (!qLinkGstElements(gstCapsFilter, gstVideoSink))
+        qCDebug(qLcMediaVideoSink) << "couldn't link caps filter and sink";
     gstVideoSink.setState(GST_STATE_PAUSED);
 
     gstPipeline.endConfig();
diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink_p.h b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink_p.h
index 76dcffb40..730f692a1 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink_p.h
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink_p.h
@@ -64,6 +64,7 @@ private:
     QGstBin sinkBin;
     QGstElement gstQueue;
     QGstElement gstPreprocess;
+    QGstElement gstCapsFilter;
     QGstElement gstVideoSink;
     QGstElement gstQtSink;
     QGstElement gstSubtitleSink;