avfilter/vignette: use AV_OPT_TYPE_BOOL for dither option

libavfilter/vf_vignette.c

@@ -90,7 +90,7 @@ static const AVOption vignette_options[] = {
     { "eval", "specify when to evaluate expressions", OFFSET(eval_mode), AV_OPT_TYPE_INT, {.i64 = EVAL_MODE_INIT}, 0, EVAL_MODE_NB-1, FLAGS, "eval" },
          { "init",  "eval expressions once during initialization", 0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_INIT},  .flags = FLAGS, .unit = "eval" },
          { "frame", "eval expressions for each frame",             0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_FRAME}, .flags = FLAGS, .unit = "eval" },
-    { "dither", "set dithering", OFFSET(do_dither), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, FLAGS },
+    { "dither", "set dithering", OFFSET(do_dither), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, FLAGS },
     { "aspect", "set aspect ratio", OFFSET(aspect), AV_OPT_TYPE_RATIONAL, {.dbl = 1}, 0, DBL_MAX, .flags = FLAGS },
     { NULL }
 };