@Georgy I wanted to try Blend Program, as you suggested, to check the various color plugins. The first one, “solid_red.bp” works fine. The second, “print_hdr.bp” does not work and the terminal shows errors that I do not understand. I don't even know how to declare a variable, although in the first function I don't have this problem. I attach the two functions and report the error on the terminal: "BlendProgramCompile: executing gcc -fPIC -O2 -shared -o /home/paz/.bcast5lib/dlfcn/bp/print_hdr.bp.so /home/paz/.bcast5lib/dlfcn/bp/print_hdr.bp.c -lm /home/paz/.bcast5lib/dlfcn/bp/print_hdr.bp: In function ‘bpProc’: /home/paz/.bcast5lib/dlfcn/bp/print_hdr.bp:11:8: error: ‘R’ undeclared (first use in this function) 11 | printf(R); | ^ /home/paz/.bcast5lib/dlfcn/bp/print_hdr.bp:11:8: note: each undeclared identifier is reported only once for each function it appears in virtual int BlendProgram::process_buffer(VFrame**, int64_t, double): Blend Program: compilation of program .bcast5lib/dlfcn/bp/print_hdr.bp failed see console printout for diagnostics" I tried with: printf(R(0)); printf(R(i)); printf(R); Always with a similar error.