patched qtmultimedia to support non interlaced camera via gstreamer see https://blog.nobugware.com/post/2018/my_own_car_system_raspberry_pi_offline_mapping/

interlace.patch

--- src/plugins/gstreamer/camerabin/camerabinsession.cpp        2018-04-25 00:21:50.000000000 -0400
+++ src/plugins/gstreamer/camerabin/camerabinsession.cpp.new    2018-06-04 09:26:55.853527569 -0400
@@ -556,6 +556,22 @@
             gst_object_unref(GST_OBJECT(camSrc));
     }
 
+
+    const QByteArray envInterlace = qgetenv("QT_GSTREAMER_CAMERABIN_VIDEO_INTERLACE");
+    if (envInterlace.length() > 0) {
+        GstElement *interlace = gst_element_factory_make ("interlace", NULL);
+        if (interlace == NULL)
+            g_error ("Could not create 'interlace' element");
+
+
+        g_object_set(G_OBJECT(m_camerabin), "viewfinder-filter", interlace, NULL);
+
+        #if CAMERABIN_DEBUG
+            qDebug() << "set camera filter" << interlace;
+        #endif
+        gst_object_unref (interlace);
+    }
+
     return m_cameraSrc;
 }
 

PKGBUILD

# $Id: PKGBUILD 240297 2015-06-03 10:22:03Z fyan $
# Maintainer: Felix Yan <felixonmars@archlinux.org>
# Contributor: Andrea Scarpino <andrea@archlinux.org>

pkgname=qt5-multimedia
_qtver=5.11.1
pkgver=${_qtver/-/}
pkgrel=1
arch=('x86_64' 'armv7h')
url='http://qt-project.org/'
license=('GPL3' 'LGPL3' 'FDL' 'custom')
pkgdesc='Classes for audio, video, radio and camera functionality'
depends=('qt5-base' 'gst-plugins-base' 'libpulse' 'openal')
makedepends=('qt5-declarative' 'gst-plugins-bad')
optdepends=('qt5-declarative: QML bindings' 'gst-plugins-good: camera support, additional plugins'
            'gst-plugins-bad: camera support, additional plugins' 'gst-plugins-ugly: additional plugins'
            'gst-libav: ffmpeg plugin')
groups=('qt' 'qt5')
_pkgfqn="${pkgname/5-/}-everywhere-src-${_qtver}"
source=("http://download.qt.io/official_releases/qt/${pkgver%.*}/${_qtver}/submodules/${_pkgfqn}.tar.xz" "interlace.patch")
sha256sums=('f28bb57890b4666a9aafaa116a30c51dedb0f23b60a510280a27eb032b58c90c'
            'c987af5a170b1f3f3363f8eb03ba07fdaca1becefab5a9458d3834c7aacd6e13')

prepare() {
 mkdir -p build
 cd $srcdir/${_pkgfqn}
 patch -Np1 -i "${srcdir}/interlace.patch"
}

build() {
  cd build

  qmake ../${_pkgfqn}
  make
}

package() {
  cd build
  make INSTALL_ROOT="$pkgdir" install

  # Drop QMAKE_PRL_BUILD_DIR because reference the build dir
  find "$pkgdir/usr/lib" -type f -name '*.prl' \
    -exec sed -i -e '/^QMAKE_PRL_BUILD_DIR/d' {} \;

  install -d "$pkgdir"/usr/share/licenses
  ln -s /usr/share/licenses/qt5-base "$pkgdir"/usr/share/licenses/${pkgname}
}