avfilter/af_apad: do not add infinite silence for zero pad_dur or whole_dur

Unfortunately pad_len and pad_dur behaviour was different if 0 was specified,
pad_dur handled 0 duration as infinity, for pad_len, infinity was -1.

Let's make the behaviour consistent by handling 0 duration for pad_dur and
whole_dur as indeed 0 duration. This somewhat changes the behaviour of the
filter if 0 was explicitly specified, but deprecating the old option and adding
a new for the corrected behaviour seemed a bit overkill. So let's document the
change instead.

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/filters.texi

@@ -2291,12 +2291,12 @@ with @option{pad_len}.
 @item pad_dur
 Specify the duration of samples of silence to add. See
 @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}
-for the accepted syntax. Used only if set to non-zero value.
+for the accepted syntax. Used only if set to non-negative value.
 
 @item whole_dur
 Specify the minimum total duration in the output audio stream. See
 @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}
-for the accepted syntax. Used only if set to non-zero value. If the value is longer than
+for the accepted syntax. Used only if set to non-negative value. If the value is longer than
 the input audio length, silence is added to the end, until the value is reached.
 This option is mutually exclusive with @option{pad_dur}
 @end table
@@ -2305,6 +2305,9 @@ If neither the @option{pad_len} nor the @option{whole_len} nor @option{pad_dur}
 nor @option{whole_dur} option is set, the filter will add silence to the end of
 the input stream indefinitely.
 
+Note that for ffmpeg 4.4 and earlier a zero @option{pad_dur} or
+@option{whole_dur} also caused the filter to add silence indefinitely.
+
 @subsection Examples
 
 @itemize

libavfilter/af_apad.c

@@ -52,8 +52,8 @@ static const AVOption apad_options[] = {
     { "packet_size", "set silence packet size",                                  OFFSET(packet_size), AV_OPT_TYPE_INT,   { .i64 = 4096 }, 0, INT_MAX, A },
     { "pad_len",     "set number of samples of silence to add",                  OFFSET(pad_len),     AV_OPT_TYPE_INT64, { .i64 = -1 }, -1, INT64_MAX, A },
     { "whole_len",   "set minimum target number of samples in the audio stream", OFFSET(whole_len),   AV_OPT_TYPE_INT64, { .i64 = -1 }, -1, INT64_MAX, A },
-    { "pad_dur",     "set duration of silence to add",                           OFFSET(pad_dur),     AV_OPT_TYPE_DURATION, { .i64 = 0 }, 0, INT64_MAX, A },
-    { "whole_dur",   "set minimum target duration in the audio stream",          OFFSET(whole_dur),   AV_OPT_TYPE_DURATION, { .i64 = 0 }, 0, INT64_MAX, A },
+    { "pad_dur",     "set duration of silence to add",                           OFFSET(pad_dur),     AV_OPT_TYPE_DURATION, { .i64 = -1 }, -1, INT64_MAX, A },
+    { "whole_dur",   "set minimum target duration in the audio stream",          OFFSET(whole_dur),   AV_OPT_TYPE_DURATION, { .i64 = -1 }, -1, INT64_MAX, A },
     { NULL }
 };
 
@@ -138,9 +138,9 @@ static int config_output(AVFilterLink *outlink)
     AVFilterContext *ctx = outlink->src;
     APadContext *s  = ctx->priv;
 
-    if (s->pad_dur)
+    if (s->pad_dur >= 0)
         s->pad_len = av_rescale(s->pad_dur, outlink->sample_rate, AV_TIME_BASE);
-    if (s->whole_dur)
+    if (s->whole_dur >= 0)
         s->whole_len = av_rescale(s->whole_dur, outlink->sample_rate, AV_TIME_BASE);
 
     s->pad_len_left   = s->pad_len;

libavfilter/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR   8
 #define LIBAVFILTER_VERSION_MINOR  16
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MICRO 102
 
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \