libavfilter/avf_showwaves: make sqrt and cbrt scale option values available to showwavespic by name

The 'sqrt' and 'cbrt' scalers were added in commit
80262d8c, but their symbolic option values
only made available to the showwaves filter, not showwavespic, despite
the scalers working properly by their numerical option values.
Signed-off-by: Moritz Barsnick <barsnick@gmx.net>

doc/filters.texi

@@ -17897,7 +17897,23 @@ Set if channels should be drawn separately or overlap. Default value is 0.
 Set colors separated by '|' which are going to be used for drawing of each channel.
 
 @item scale
-Set amplitude scale. Can be linear @code{lin} or logarithmic @code{log}.
+Set amplitude scale.
+
+Available values are:
+@table @samp
+@item lin
+Linear.
+
+@item log
+Logarithmic.
+
+@item sqrt
+Square root.
+
+@item cbrt
+Cubic root.
+@end table
+
 Default is linear.
 @end table
 

libavfilter/avf_showwaves.c

@@ -676,6 +676,8 @@ static const AVOption showwavespic_options[] = {
     { "scale", "set amplitude scale", OFFSET(scale), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, SCALE_NB-1, FLAGS, .unit="scale" },
         { "lin", "linear",         0, AV_OPT_TYPE_CONST, {.i64=SCALE_LIN}, .flags=FLAGS, .unit="scale"},
         { "log", "logarithmic",    0, AV_OPT_TYPE_CONST, {.i64=SCALE_LOG}, .flags=FLAGS, .unit="scale"},
+        { "sqrt", "square root",   0, AV_OPT_TYPE_CONST, {.i64=SCALE_SQRT}, .flags=FLAGS, .unit="scale"},
+        { "cbrt", "cubic root",    0, AV_OPT_TYPE_CONST, {.i64=SCALE_CBRT}, .flags=FLAGS, .unit="scale"},
     { NULL }
 };