select: new filter to drop frames based on offset and skip

Motivation was to select only odd or even frames.

gst/select/gstselect.h

@@ -0,0 +1,71 @@
+/* GStreamer
+ * Copyright (C) <1999> Erik Walthinsen <omega@cse.ogi.edu>
+ * Copyright (C) <2003> David Schleef <ds@schleef.org>
+ * Copyright (C) 2003 Arwed v. Merkatz <v.merkatz@gmx.net>
+ * Copyright (C) 2006 Mark Nauwelaerts <manauw@skynet.be>
+ * Copyright (C) 2015 United States Government, Joshua M. Doe <oss@nvl.army.mil>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+
+#ifndef __GST_SELECT_H__
+#define __GST_SELECT_H__
+
+#include <gst/base/gstbasetransform.h>
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_SELECT \
+  (gst_select_get_type())
+#define GST_SELECT(obj) \
+  (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_SELECT,GstSelect))
+#define GST_SELECT_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_SELECT,GstSelectClass))
+#define GST_IS_SELECT(obj) \
+  (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_SELECT))
+#define GST_IS_SELECT_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_SELECT))
+
+typedef struct _GstSelect GstSelect;
+typedef struct _GstSelectClass GstSelectClass;
+
+/**
+* GstSelect:
+* @element: the parent element.
+*
+*
+* The opaque GstSelect data structure.
+*/
+struct _GstSelect
+{
+  GstBaseTransform element;
+
+  /* properties */
+  gint offset;
+  gint skip;
+};
+
+struct _GstSelectClass
+{
+  GstBaseTransformClass parent_class;
+};
+
+GType gst_select_get_type(void);
+
+G_END_DECLS
+
+#endif /* __GST_SELECT_H__ */