Add asrc_anullsrc - null audio source.

Based on a patch by "S.N. Hemanth Meenakshisundaram" smeenaks!ucsd!edu.

Originally committed as revision 25188 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/filters.texi

@@ -14,6 +14,40 @@ Pass the audio source unchanged to the output.
 
 @c man end AUDIO FILTERS
 
+@chapter Audio Sources
+@c man begin AUDIO SOURCES
+
+Below is a description of the currently available audio sources.
+
+@section anullsrc
+
+Null audio source, never return audio frames. It is mainly useful as a
+template and to be employed in analysis / debugging tools.
+
+It accepts as optional parameter a string of the form
+@var{sample_rate}:@var{channel_layout}.
+
+@var{sample_rate} specify the sample rate, and defaults to 44100.
+
+@var{channel_layout} specify the channel layout, and can be either an
+integer or a string representing a channel layout. The default value
+of @var{channel_layout} is 3, which corresponds to CH_LAYOUT_STEREO.
+
+Check the channel_layout_map definition in
+@file{libavcodec/audioconvert.c} for the correspondance between string
+and channel layout values.
+
+Follow some examples:
+@example
+#  set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
+anullsrc=48000:4
+
+# same as
+anullsrc=48000:mono
+@end example
+
+@c man end AUDIO SOURCES
+
 @chapter Video Filters
 @c man begin VIDEO FILTERS
 

libavfilter/Makefile

@@ -16,6 +16,8 @@ OBJS = allfilters.o                                                     \
 
 OBJS-$(CONFIG_ANULL_FILTER)                  += af_anull.o
 
+OBJS-$(CONFIG_ANULLSRC_FILTER)               += asrc_anullsrc.o
+
 OBJS-$(CONFIG_ASPECT_FILTER)                 += vf_aspect.o
 OBJS-$(CONFIG_CROP_FILTER)                   += vf_crop.o
 OBJS-$(CONFIG_FIFO_FILTER)                   += vf_fifo.o

libavfilter/allfilters.c

@@ -36,6 +36,8 @@ void avfilter_register_all(void)
 
     REGISTER_FILTER (ANULL,       anull,       af);
 
+    REGISTER_FILTER (ANULLSRC,    anullsrc,    asrc);
+
     REGISTER_FILTER (ASPECT,      aspect,      vf);
     REGISTER_FILTER (CROP,        crop,        vf);
     REGISTER_FILTER (FIFO,        fifo,        vf);

libavfilter/asrc_anullsrc.c

@@ -0,0 +1,96 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * null audio source
+ */
+
+#include "avfilter.h"
+#include "libavcodec/audioconvert.h"
+
+typedef struct {
+    int64_t channel_layout;
+    int64_t sample_rate;
+} ANullContext;
+
+static int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    ANullContext *priv = ctx->priv;
+    char channel_layout_str[128] = "";
+
+    priv->sample_rate = 44100;
+    priv->channel_layout = CH_LAYOUT_STEREO;
+
+    if (args)
+        sscanf(args, "%"PRId64":%s", &priv->sample_rate, channel_layout_str);
+
+    if (priv->sample_rate < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Invalid negative sample rate: %"PRId64"\n", priv->sample_rate);
+        return AVERROR(EINVAL);
+    }
+
+    if (*channel_layout_str)
+        if (!(priv->channel_layout = avcodec_get_channel_layout(channel_layout_str))
+            && sscanf(channel_layout_str, "%"PRId64, &priv->channel_layout) != 1) {
+            av_log(ctx, AV_LOG_ERROR, "Invalid value '%s' for channel layout\n",
+                   channel_layout_str);
+            return AVERROR(EINVAL);
+        }
+
+    return 0;
+}
+
+static int config_props(AVFilterLink *outlink)
+{
+    ANullContext *priv = outlink->src->priv;
+    char buf[128];
+    int chans_nb;
+
+    outlink->sample_rate = priv->sample_rate;
+    outlink->channel_layout = priv->channel_layout;
+
+    chans_nb = avcodec_channel_layout_num_channels(priv->channel_layout);
+    avcodec_get_channel_layout_string(buf, sizeof(buf), chans_nb, priv->channel_layout);
+    av_log(outlink->src, AV_LOG_INFO,
+           "sample_rate:%"PRId64 " channel_layout:%"PRId64 " channel_layout_description:'%s'\n",
+           priv->sample_rate, priv->channel_layout, buf);
+
+    return 0;
+}
+
+static int request_frame(AVFilterLink *link)
+{
+    return -1;
+}
+
+AVFilter avfilter_asrc_anullsrc = {
+    .name        = "anullsrc",
+    .description = NULL_IF_CONFIG_SMALL("Null audio source, never return audio frames."),
+
+    .init        = init,
+    .priv_size   = sizeof(ANullContext),
+
+    .inputs      = (AVFilterPad[]) {{ .name = NULL}},
+
+    .outputs     = (AVFilterPad[]) {{ .name = "default",
+                                      .type = AVMEDIA_TYPE_AUDIO,
+                                      .config_props = config_props,
+                                      .request_frame = request_frame, },
+                                    { .name = NULL}},
+};

libavfilter/avfilter.h

@@ -25,7 +25,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  1
-#define LIBAVFILTER_VERSION_MINOR 42
+#define LIBAVFILTER_VERSION_MINOR 43
 #define LIBAVFILTER_VERSION_MICRO  0
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \