Add the null video filter.

Originally committed as revision 20275 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vf_null.c

@@ -0,0 +1,56 @@
+/*
+ * 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/vf_null.c
+ * null filter
+ */
+
+#include "avfilter.h"
+
+static AVFilterPicRef *get_video_buffer(AVFilterLink *link, int perms, int w, int h)
+{
+    return avfilter_get_video_buffer(link->dst->outputs[0], perms, w, h);
+}
+
+static void start_frame(AVFilterLink *link, AVFilterPicRef *picref)
+{
+    avfilter_start_frame(link->dst->outputs[0], picref);
+}
+
+static void end_frame(AVFilterLink *link)
+{
+    avfilter_end_frame(link->dst->outputs[0]);
+}
+
+AVFilter avfilter_vf_null = {
+    .name      = "null",
+
+    .priv_size = 0,
+
+    .inputs    = (AVFilterPad[]) {{ .name             = "default",
+                                    .type             = CODEC_TYPE_VIDEO,
+                                    .get_video_buffer = get_video_buffer,
+                                    .start_frame      = start_frame,
+                                    .end_frame        = end_frame },
+                                  { .name = NULL}},
+
+    .outputs   = (AVFilterPad[]) {{ .name             = "default",
+                                    .type             = CODEC_TYPE_VIDEO, },
+                                  { .name = NULL}},
+};