cmdutils: allow -h filter=<name> to print information about a filter.

cmdutils.c

@@ -1268,6 +1268,44 @@ static void show_help_muxer(const char *name)
         show_help_children(fmt->priv_class, AV_OPT_FLAG_ENCODING_PARAM);
 }
 
+static void show_help_filter(const char *name)
+{
+    const AVFilter *f = avfilter_get_by_name(name);
+    int i, count;
+
+    if (!name) {
+        av_log(NULL, AV_LOG_ERROR, "No filter name specified.\n");
+        return;
+    } else if (!f) {
+        av_log(NULL, AV_LOG_ERROR, "Unknown filter '%s'.\n", name);
+        return;
+    }
+
+    printf("Filter %s [%s]:\n", f->name, f->description);
+
+    printf("    Inputs:\n");
+    count = avfilter_pad_count(f->inputs);
+    for (i = 0; i < count; i++) {
+        printf("        %d %s (%s)\n", i, avfilter_pad_get_name(f->inputs, i),
+               media_type_string(avfilter_pad_get_type(f->inputs, i)));
+    }
+    if (f->flags & AVFILTER_FLAG_DYNAMIC_INPUTS)
+        printf("        dynamic (depending on the options)\n");
+
+    printf("    Outputs:\n");
+    count = avfilter_pad_count(f->outputs);
+    for (i = 0; i < count; i++) {
+        printf("        %d %s (%s)\n", i, avfilter_pad_get_name(f->outputs, i),
+               media_type_string(avfilter_pad_get_type(f->outputs, i)));
+    }
+    if (f->flags & AVFILTER_FLAG_DYNAMIC_OUTPUTS)
+        printf("        dynamic (depending on the options)\n");
+
+    if (f->priv_class)
+        show_help_children(f->priv_class, AV_OPT_FLAG_VIDEO_PARAM |
+                                          AV_OPT_FLAG_AUDIO_PARAM);
+}
+
 int show_help(void *optctx, const char *opt, const char *arg)
 {
     char *topic, *par;
@@ -1288,6 +1326,8 @@ int show_help(void *optctx, const char *opt, const char *arg)
         show_help_demuxer(par);
     } else if (!strcmp(topic, "muxer")) {
         show_help_muxer(par);
+    } else if (!strcmp(topic, "filter")) {
+        show_help_filter(par);
     } else {
         show_help_default(topic, par);
     }

doc/avtools-common-opts.texi

@@ -74,6 +74,10 @@ Print detailed information about the demuxer named @var{demuxer_name}. Use the
 Print detailed information about the muxer named @var{muxer_name}. Use the
 @option{-formats} option to get a list of all muxers and demuxers.
 
+@item filter=@var{filter_name}
+Print detailed information about the filter name @var{filter_name}. Use the
+@option{-filters} option to get a list of all filters.
+
 @end table
 
 @item -version