avfilter: document mono option of silencedetect filter

Also provide shorter option, and reorder options in documentation.

doc/filters.texi

@@ -4171,12 +4171,15 @@ The printed times and duration are expressed in seconds.
 The filter accepts the following options:
 
 @table @option
-@item duration, d
-Set silence duration until notification (default is 2 seconds).
-
 @item noise, n
 Set noise tolerance. Can be specified in dB (in case "dB" is appended to the
 specified value) or amplitude ratio. Default is -60dB, or 0.001.
+
+@item duration, d
+Set silence duration until notification (default is 2 seconds).
+
+@item mono, m
+Process each channel separately, instead of combined. By default is disabled.
 @end table
 
 @subsection Examples

libavfilter/af_silencedetect.c

@@ -57,7 +57,8 @@ static const AVOption silencedetect_options[] = {
     { "noise",     "set noise tolerance",              OFFSET(noise),     AV_OPT_TYPE_DOUBLE, {.dbl=0.001},          0, DBL_MAX,  FLAGS },
     { "d",         "set minimum duration in seconds",  OFFSET(duration),  AV_OPT_TYPE_DOUBLE, {.dbl=2.},             0, 24*60*60, FLAGS },
     { "duration",  "set minimum duration in seconds",  OFFSET(duration),  AV_OPT_TYPE_DOUBLE, {.dbl=2.},             0, 24*60*60, FLAGS },
-    { "mono",      "check each channel separately",    OFFSET(mono),      AV_OPT_TYPE_BOOL,   {.i64=0.},             0, 1, FLAGS },
+    { "mono",      "check each channel separately",    OFFSET(mono),      AV_OPT_TYPE_BOOL,   {.i64=0.},             0, 1,        FLAGS },
+    { "m",         "check each channel separately",    OFFSET(mono),      AV_OPT_TYPE_BOOL,   {.i64=0.},             0, 1,        FLAGS },
     { NULL }
 };