asrc_anullsrc: extend syntax to make it accept a non positional list of arguments

The new syntax is more extensible and more user-friendly.

This breaks the previous syntax, should not be an issue as possibly
no-one is already using anullsrc.

doc/filters.texi

@@ -312,26 +312,34 @@ value is "-1".
 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}.
+It accepts an optional sequence of @var{key}=@var{value} pairs,
+separated by ":".
+
+The description of the accepted options follows.
 
-@var{sample_rate} specify the sample rate, and defaults to 44100.
+@table @option
+
+@item sample_rate, s
+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.
+@item channel_layout, cl
+
+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 "stereo".
 
 Check the channel_layout_map definition in
 @file{libavcodec/audioconvert.c} for the mapping between strings and
 channel layout values.
+@end table
 
 Follow some examples:
 @example
-#  set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
-anullsrc=48000:4
+#  set the sample rate to 48000 Hz and the channel layout to AV_CH_LAYOUT_MONO.
+anullsrc=r=48000:cl=4
 
 # same as
-anullsrc=48000:mono
+anullsrc=r=48000:cl=mono
 @end example
 
 @c man end AUDIO SOURCES

libavfilter/asrc_anullsrc.c

@@ -21,37 +21,61 @@
  * null audio source
  */
 
-#include "avfilter.h"
 #include "libavutil/audioconvert.h"
+#include "libavutil/opt.h"
+
+#include "avfilter.h"
+#include "internal.h"
 
 typedef struct {
+    const AVClass *class;
+    char   *channel_layout_str;
     int64_t channel_layout;
-    int64_t sample_rate;
+    char   *sample_rate_str;
+    int     sample_rate;
 } ANullContext;
 
+#define OFFSET(x) offsetof(ANullContext, x)
+
+static const AVOption anullsrc_options[]= {
+    { "channel_layout", "set channel_layout", OFFSET(channel_layout_str), FF_OPT_TYPE_STRING, {.str = "stereo"}, 0, 0 },
+    { "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 },
+    { NULL },
+};
+
+static const char *anullsrc_get_name(void *ctx)
+{
+    return "anullsrc";
+}
+
+static const AVClass anullsrc_class = {
+    "ANullSrcContext",
+    anullsrc_get_name,
+    anullsrc_options
+};
+
 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 = AV_CH_LAYOUT_STEREO;
+    int ret;
 
-    if (args)
-        sscanf(args, "%"PRId64":%s", &priv->sample_rate, channel_layout_str);
+    priv->class = &anullsrc_class;
+    av_opt_set_defaults(priv);
 
-    if (priv->sample_rate < 0) {
-        av_log(ctx, AV_LOG_ERROR, "Invalid negative sample rate: %"PRId64"\n", priv->sample_rate);
-        return AVERROR(EINVAL);
+    if ((ret = (av_set_options_string(priv, args, "=", ":"))) < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Error parsing options string: '%s'\n", args);
+        return ret;
     }
 
-    if (*channel_layout_str)
-        if (!(priv->channel_layout = av_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);
-        }
+    if ((ret = ff_parse_sample_rate(&priv->sample_rate,
+                                     priv->sample_rate_str, ctx)) < 0)
+        return ret;
+
+    if ((ret = ff_parse_channel_layout(&priv->channel_layout,
+                                        priv->channel_layout_str, ctx)) < 0)
+        return ret;
 
     return 0;
 }
@@ -68,7 +92,7 @@ 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:%"PRId64 " channel_layout:%"PRId64 " channel_layout_description:'%s'\n",
+           "sample_rate:%d channel_layout:%"PRId64 " channel_layout_description:'%s'\n",
            priv->sample_rate, priv->channel_layout, buf);
 
     return 0;

libavfilter/avfilter.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  2
 #define LIBAVFILTER_VERSION_MINOR 43
-#define LIBAVFILTER_VERSION_MICRO  0
+#define LIBAVFILTER_VERSION_MICRO  1
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \