Implement null video source.

Originally committed as revision 21240 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vsrc_nullsrc.c

@@ -0,0 +1,83 @@
+/*
+ * 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 libavfilter/vsrc_nullsrc.c
+ * null video source
+ */
+
+#include "avfilter.h"
+
+typedef struct {
+    int w, h;
+} NullContext;
+
+static int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    NullContext *priv = ctx->priv;
+
+    priv->w = 352;
+    priv->h = 288;
+
+    if (args)
+        sscanf(args, "%d:%d", &priv->w, &priv->h);
+
+    if (priv->w <= 0 || priv->h <= 0) {
+        av_log(ctx, AV_LOG_ERROR, "Non-positive size values are not acceptable.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int config_props(AVFilterLink *outlink)
+{
+    NullContext *priv = outlink->src->priv;
+
+    outlink->w = priv->w;
+    outlink->h = priv->h;
+
+    av_log(outlink->src, AV_LOG_INFO, "w:%d h:%d\n", priv->w, priv->h);
+
+    return 0;
+}
+
+static int request_frame(AVFilterLink *link)
+{
+    return -1;
+}
+
+AVFilter avfilter_vsrc_nullsrc = {
+    .name        = "nullsrc",
+    .description = "Null video source, never return images.",
+
+    .init       = init,
+    .priv_size = sizeof(NullContext),
+
+    .inputs    = (AVFilterPad[]) {{ .name = NULL}},
+
+    .outputs   = (AVFilterPad[]) {
+        {
+            .name            = "default",
+            .type            = CODEC_TYPE_VIDEO,
+            .config_props    = config_props,
+            .request_frame   = request_frame,
+        },
+        { .name = NULL}
+    },
+};