VAR_BRIGHTNESS    122 libavfilter/vf_eq.c     eq->var_values[VAR_BRIGHTNESS] =  av_clipf(av_expr_eval(eq->brightness_pexpr, eq->var_values, eq), -1.0, 1.0);
VAR_BRIGHTNESS    123 libavfilter/vf_eq.c     eq->param[0].brightness = eq->var_values[VAR_BRIGHTNESS];