@@ -309,8 +309,10 @@ value is "-1".

 @section anullsrc

-Null audio source, never return audio frames. It is mainly useful as a

-template and to be employed in analysis / debugging tools.

+Null audio source, return unprocessed audio frames. It is mainly useful

+as a template and to be employed in analysis / debugging tools, or as

+the source for filters which ignore the input data (for example the sox

+synth filter).

 It accepts an optional sequence of @var{key}=@var{value} pairs,

 separated by ":".

@@ -331,6 +333,10 @@ is "stereo".

 Check the channel_layout_map definition in

 @file{libavcodec/audioconvert.c} for the mapping between strings and

 channel layout values.

+

+@item nb_samples, n

+Set the number of samples per requested frames.

+

 @end table

 Follow some examples:

@@ -33,6 +33,8 @@ typedef struct {

     int64_t channel_layout;

     char   *sample_rate_str;

     int     sample_rate;

+    int nb_samples;             ///< number of samples per requested frame

+    int64_t pts;

 } ANullContext;

 #define OFFSET(x) offsetof(ANullContext, x)

@@ -42,6 +44,8 @@ static const AVOption anullsrc_options[]= {

     { "cl",             "set channel_layout", OFFSET(channel_layout_str), FF_OPT_TYPE_STRING, {.str = "stereo"}, 0, 0 },

     { "sample_rate",    "set sample rate",    OFFSET(sample_rate_str)   , FF_OPT_TYPE_STRING, {.str = "44100"}, 0, 0 },

     { "r",              "set sample rate",    OFFSET(sample_rate_str)   , FF_OPT_TYPE_STRING, {.str = "44100"}, 0, 0 },

+    { "nb_samples",     "set the number of samples per requested frame", OFFSET(nb_samples), FF_OPT_TYPE_INT, {.dbl = 1024}, 0, INT_MAX },

+    { "n",              "set the number of samples per requested frame", OFFSET(nb_samples), FF_OPT_TYPE_INT, {.dbl = 1024}, 0, INT_MAX },

     { NULL },

 };

@@ -92,15 +96,29 @@ static int config_props(AVFilterLink *outlink)

     chans_nb = av_get_channel_layout_nb_channels(priv->channel_layout);

     av_get_channel_layout_string(buf, sizeof(buf), chans_nb, priv->channel_layout);

     av_log(outlink->src, AV_LOG_INFO,

-           "sample_rate:%d channel_layout:%"PRId64 " channel_layout_description:'%s'\n",

-           priv->sample_rate, priv->channel_layout, buf);

+           "sample_rate:%d channel_layout:%"PRId64 " channel_layout_description:'%s' nb_samples:%d\n",

+           priv->sample_rate, priv->channel_layout, buf, priv->nb_samples);

     return 0;

 }

-static int request_frame(AVFilterLink *link)

+static int request_frame(AVFilterLink *outlink)

 {

-    return -1;

+    ANullContext *null = outlink->src->priv;

+    AVFilterBufferRef *samplesref;

+

+    samplesref =

+        avfilter_get_audio_buffer(outlink, AV_PERM_WRITE, null->nb_samples);

+    samplesref->pts = null->pts;

+    samplesref->pos = -1;

+    samplesref->audio->channel_layout = null->channel_layout;

+    samplesref->audio->sample_rate = outlink->sample_rate;

+

+    avfilter_filter_samples(outlink, avfilter_ref_buffer(samplesref, ~0));

+    avfilter_unref_buffer(samplesref);

+

+    null->pts += null->nb_samples;

+    return 0;

 }

 AVFilter avfilter_asrc_anullsrc = {

@@ -30,7 +30,7 @@

 #define LIBAVFILTER_VERSION_MAJOR  2

 #define LIBAVFILTER_VERSION_MINOR 43

-#define LIBAVFILTER_VERSION_MICRO  1

+#define LIBAVFILTER_VERSION_MICRO  2

 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \

                                                LIBAVFILTER_VERSION_MINOR, \