Since gnuradio relies on SDL (version 1) the video sink of gnuradio does not work on macOS Mojave and Catalina. This is a simple workaround to have a video sink working on macOS > 10.14. with SDL2.
First, create a named pipe:
mkfifo /Users/<name>/stdout
Compile and open SDLDisplay:
make
./SDLDisplay -i /Users/kesenheimer/stdout -h 512 -w 512
Use the file sink of gnuradio to write to the named pipe. File sink properties:
File: /Users/<name>/stdout
Unbuffered: On
Append File: Append
Use video_sdl_test.grc as starting point.
sudo port install libsdl2 libsdl2_gfx libsdl2_image libsdl2_mixer