lavfi: add vsink_buffer, and use it in ff* tools

Also add the public interface libavfilter/vsink_buffer.h.

libavfilter/vsink_buffer.h

@@ -0,0 +1,47 @@
+/*
+ * 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
+ */
+
+#ifndef AVFILTER_VSINK_BUFFER_H
+#define AVFILTER_VSINK_BUFFER_H
+
+/**
+ * @file
+ * memory buffer sink API for video
+ */
+
+#include "avfilter.h"
+
+/**
+ * Tell av_vsink_buffer_get_video_buffer_ref() to read the picref, but not
+ * remove it from the buffer. This is useful if you need only to read
+ * the picref, without to fetch it.
+ */
+#define AV_VSINK_BUF_FLAG_PEEK 1
+
+/**
+ * Get a video buffer data from buffer_sink and put it in picref.
+ *
+ * @param buffer_sink pointer to a buffer sink context
+ * @param flags a combination of AV_VSINK_BUF_FLAG_* flags
+ * @return >= 0 in case of success, a negative AVERROR code in case of
+ * failure
+ */
+int av_vsink_buffer_get_video_buffer_ref(AVFilterContext *buffer_sink,
+                                         AVFilterBufferRef **picref, int flags);
+
+#endif /* AVFILTER_VSINK_BUFFER_H */