avfilter/af_compand: fix default companding to avoid clipping

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

doc/filters.texi

@@ -2080,7 +2080,7 @@ the following syntax: @code{x0/y0|x1/y1|x2/y2|....} or
 The input values must be in strictly increasing order but the transfer function
 does not have to be monotonically rising. The point @code{0/0} is assumed but
 may be overridden (by @code{0/out-dBn}). Typical values for the transfer
-function are @code{-70/-70|-60/-20}.
+function are @code{-70/-70|-60/-20|1/0}.
 
 @item soft-knee
 Set the curve radius in dB for all joints. It defaults to 0.01.

libavfilter/af_compand.c

@@ -74,7 +74,7 @@ typedef struct CompandContext {
 static const AVOption compand_options[] = {
     { "attacks", "set time over which increase of volume is determined", OFFSET(attacks), AV_OPT_TYPE_STRING, { .str = "0.3" }, 0, 0, A },
     { "decays", "set time over which decrease of volume is determined", OFFSET(decays), AV_OPT_TYPE_STRING, { .str = "0.8" }, 0, 0, A },
-    { "points", "set points of transfer function", OFFSET(points), AV_OPT_TYPE_STRING, { .str = "-70/-70|-60/-20" }, 0, 0, A },
+    { "points", "set points of transfer function", OFFSET(points), AV_OPT_TYPE_STRING, { .str = "-70/-70|-60/-20|1/0" }, 0, 0, A },
     { "soft-knee", "set soft-knee", OFFSET(curve_dB), AV_OPT_TYPE_DOUBLE, { .dbl = 0.01 }, 0.01, 900, A },
     { "gain", "set output gain", OFFSET(gain_dB), AV_OPT_TYPE_DOUBLE, { .dbl = 0 }, -900, 900, A },
     { "volume", "set initial volume", OFFSET(initial_volume), AV_OPT_TYPE_DOUBLE, { .dbl = 0 }, -900, 0, A },