package/ffmpeg: add optional support for OpenCV4

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/ffmpeg/ffmpeg.mk

@@ -297,6 +297,10 @@ endif
 ifeq ($(BR2_PACKAGE_OPENCV3_LIB_IMGPROC)x$(BR2_PACKAGE_OPENCV3_WITH_FFMPEG),yx)
 FFMPEG_CONF_OPTS += --enable-libopencv
 FFMPEG_DEPENDENCIES += opencv3
+else ifeq ($(BR2_PACKAGE_OPENCV4_LIB_IMGPROC)x$(BR2_PACKAGE_OPENCV4_WITH_FFMPEG),yx)
+FFMPEG_CONF_OPTS += --enable-libopencv \
+	--extra-cflags=-I$(STAGING_DIR)/usr/include/opencv4
+FFMPEG_DEPENDENCIES += opencv4
 else
 FFMPEG_CONF_OPTS += --disable-libopencv
 endif