lavfi/scale: add nb_slices debug option

libavfilter/vf_scale.c

@@ -110,6 +110,8 @@ typedef struct ScaleContext {
     int in_v_chr_pos;
 
     int force_original_aspect_ratio;
+
+    int nb_slices;
 } ScaleContext;
 
 AVFilter ff_vf_scale2ref;
@@ -575,6 +577,15 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
     if(scale->interlaced>0 || (scale->interlaced<0 && in->interlaced_frame)){
         scale_slice(link, out, in, scale->isws[0], 0, (link->h+1)/2, 2, 0);
         scale_slice(link, out, in, scale->isws[1], 0,  link->h   /2, 2, 1);
+    }else if (scale->nb_slices) {
+        int i, slice_h, slice_start, slice_end = 0;
+        const int nb_slices = FFMIN(scale->nb_slices, link->h);
+        for (i = 0; i < nb_slices; i++) {
+            slice_start = slice_end;
+            slice_end   = (link->h * (i+1)) / nb_slices;
+            slice_h     = slice_end - slice_start;
+            scale_slice(link, out, in, scale->sws, slice_start, slice_h, 1, 0);
+        }
     }else{
         scale_slice(link, out, in, scale->sws, 0, link->h, 1, 0);
     }
@@ -651,6 +662,7 @@ static const AVOption scale_options[] = {
     { "increase", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = 2 }, 0, 0, FLAGS, "force_oar" },
     { "param0", "Scaler param 0",             OFFSET(param[0]),  AV_OPT_TYPE_DOUBLE, { .dbl = SWS_PARAM_DEFAULT  }, INT_MIN, INT_MAX, FLAGS },
     { "param1", "Scaler param 1",             OFFSET(param[1]),  AV_OPT_TYPE_DOUBLE, { .dbl = SWS_PARAM_DEFAULT  }, INT_MIN, INT_MAX, FLAGS },
+    { "nb_slices", "set the number of slices (debug purpose only)", OFFSET(nb_slices), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, FLAGS },
     { NULL }
 };