qt6/qtmultimedia enable FFmpeg backend by default

I would suggest to set the ffmpeg backend as default on OpenBSD as it is
on Linux/Win/Android/Mac

OK?

diff --git a/x11/qt6/qtmultimedia/Makefile b/x11/qt6/qtmultimedia/Makefile
index 9c292166897..68ba2c5678c 100644
--- a/x11/qt6/qtmultimedia/Makefile
+++ b/x11/qt6/qtmultimedia/Makefile
@@ -1,6 +1,7 @@
QT6NAME = QtMultimedia
COMMENT = Qt6 multimedia components
PKGSPEC = qt6-qtmultimedia-${QT6_PKGSPEC}
+REVISION = 0

SHARED_LIBS += Qt6Multimedia 7.0 # 6.7
SHARED_LIBS += Qt6MultimediaQuick 5.0 # 6.7
diff --git a/x11/qt6/qtmultimedia/patches/patch-src_multimedia_platform_qplatformmediaintegration_cpp b/x11/qt6/qtmultimedia/patches/patch-src_multimedia_platform_qplatformmediaintegration_cpp
new file mode 100644
index 00000000000..f077a02aab3
--- /dev/null
+++ b/x11/qt6/qtmultimedia/patches/patch-src_multimedia_platform_qplatformmediaintegration_cpp
@@ -0,0 +1,12 @@
+Index: src/multimedia/platform/qplatformmediaintegration.cpp
+--- src/multimedia/platform/qplatformmediaintegration.cpp.orig
++++ src/multimedia/platform/qplatformmediaintegration.cpp
+@@ -49,7 +49,7 @@ static QString defaultBackend(const QStringList &backe
+ return backend;
+