item B: -DOPENCV_FFMPEG_ENABLE_LIBAVDEVICE=OFF (optional lib's empty version var disables HAVE_FFMPEG despite FFMPEG_FOUND=1)

Author: Sunrisepeak

.github/workflows/snapshot-windows-opencv.yml

@@ -88,7 +88,7 @@ jobs:
             -DBUILD_LIST=core,imgproc,imgcodecs,highgui,videoio \
             -DBUILD_SHARED_LIBS=OFF -DBUILD_ZLIB=ON -DBUILD_PNG=ON -DBUILD_JPEG=ON \
             -DENABLE_LIBJPEG_TURBO_SIMD=OFF \
-            -DWITH_FFMPEG=ON -DOPENCV_FFMPEG_SKIP_DOWNLOAD=ON \
+            -DWITH_FFMPEG=ON -DOPENCV_FFMPEG_SKIP_DOWNLOAD=ON -DOPENCV_FFMPEG_ENABLE_LIBAVDEVICE=OFF \
             -DWITH_WIN32UI=OFF -DWITH_DSHOW=OFF -DWITH_MSMF=OFF -DWITH_MSMF_DXVA=OFF \
             -DWITH_TIFF=OFF -DWITH_WEBP=OFF -DWITH_OPENJPEG=OFF -DWITH_JASPER=OFF \
             -DWITH_OPENEXR=OFF -DWITH_AVIF=OFF -DWITH_JPEGXL=OFF -DWITH_IMGCODEC_GIF=OFF \