@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 ":".
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:
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)
{ "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 },
};
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 = {