avfilter/avf_showspectrum: add 4th and 5th root scaler

Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -14640,6 +14640,10 @@ linear
 square root, default
 @item cbrt
 cubic root
+@item 4thrt
+4th root
+@item 5thrt
+5th root
 @item log
 logarithmic
 @end table
@@ -14764,6 +14768,10 @@ linear
 square root, default
 @item cbrt
 cubic root
+@item 4thrt
+4th root
+@item 5thrt
+5th root
 @item log
 logarithmic
 @end table

libavfilter/avf_showspectrum.c

@@ -40,7 +40,7 @@
 #include "window_func.h"
 
 enum DisplayMode  { COMBINED, SEPARATE, NB_MODES };
-enum DisplayScale { LINEAR, SQRT, CBRT, LOG, NB_SCALES };
+enum DisplayScale { LINEAR, SQRT, CBRT, LOG, FOURTHRT, FIFTHRT, NB_SCALES };
 enum ColorMode    { CHANNEL, INTENSITY, RAINBOW, MORELAND, NEBULAE, FIRE, FIERY, NB_CLMODES };
 enum SlideMode    { REPLACE, SCROLL, FULLFRAME, RSCROLL, NB_SLIDES };
 enum Orientation  { VERTICAL, HORIZONTAL, NB_ORIENTATIONS };
@@ -100,6 +100,8 @@ static const AVOption showspectrum_options[] = {
     { "scale", "set display scale", OFFSET(scale), AV_OPT_TYPE_INT, {.i64=SQRT}, LINEAR, NB_SCALES-1, FLAGS, "scale" },
         { "sqrt", "square root", 0, AV_OPT_TYPE_CONST, {.i64=SQRT},   0, 0, FLAGS, "scale" },
         { "cbrt", "cubic root",  0, AV_OPT_TYPE_CONST, {.i64=CBRT},   0, 0, FLAGS, "scale" },
+        { "4thrt","4th root",    0, AV_OPT_TYPE_CONST, {.i64=FOURTHRT}, 0, 0, FLAGS, "scale" },
+        { "5thrt","5th root",    0, AV_OPT_TYPE_CONST, {.i64=FIFTHRT},  0, 0, FLAGS, "scale" },
         { "log",  "logarithmic", 0, AV_OPT_TYPE_CONST, {.i64=LOG},    0, 0, FLAGS, "scale" },
         { "lin",  "linear",      0, AV_OPT_TYPE_CONST, {.i64=LINEAR}, 0, 0, FLAGS, "scale" },
     { "saturation", "color saturation multiplier", OFFSET(saturation), AV_OPT_TYPE_FLOAT, {.dbl = 1}, -10, 10, FLAGS },
@@ -568,6 +570,12 @@ static int plot_spectrum_column(AVFilterLink *inlink, AVFrame *insamples)
             case CBRT:
                 a = cbrt(a);
                 break;
+            case FOURTHRT:
+                a = pow(a, 0.25);
+                break;
+            case FIFTHRT:
+                a = pow(a, 0.20);
+                break;
             case LOG:
                 a = 1 + log10(FFMAX(FFMIN(1, a), 1e-6)) / 5; // zero = -120dBFS
                 break;
@@ -778,6 +786,8 @@ static const AVOption showspectrumpic_options[] = {
     { "scale", "set display scale", OFFSET(scale), AV_OPT_TYPE_INT, {.i64=LOG}, 0, NB_SCALES-1, FLAGS, "scale" },
         { "sqrt", "square root", 0, AV_OPT_TYPE_CONST, {.i64=SQRT},   0, 0, FLAGS, "scale" },
         { "cbrt", "cubic root",  0, AV_OPT_TYPE_CONST, {.i64=CBRT},   0, 0, FLAGS, "scale" },
+        { "4thrt","4th root",    0, AV_OPT_TYPE_CONST, {.i64=FOURTHRT}, 0, 0, FLAGS, "scale" },
+        { "5thrt","5th root",    0, AV_OPT_TYPE_CONST, {.i64=FIFTHRT},  0, 0, FLAGS, "scale" },
         { "log",  "logarithmic", 0, AV_OPT_TYPE_CONST, {.i64=LOG},    0, 0, FLAGS, "scale" },
         { "lin",  "linear",      0, AV_OPT_TYPE_CONST, {.i64=LINEAR}, 0, 0, FLAGS, "scale" },
     { "saturation", "color saturation multiplier", OFFSET(saturation), AV_OPT_TYPE_FLOAT, {.dbl = 1}, -10, 10, FLAGS },