Add support for reading YUV4MPEG2 files to ivfenc.

A large collection of example files may be found at
 http://media.xiph.org/video/derf/
This also fixes a bug in ivfenc for uncompressed IVF input, which previously
 appeared not to skip past the file header the second time it opened the file.
I don't actually have an IVF file with which to test this fix, however.

Change-Id: Id69a1e11a3fa16c4a4fa8944e880bcea090cd52b

y4minput.h

@@ -0,0 +1,59 @@
+/*
+ *  Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license and patent
+ *  grant that can be found in the LICENSE file in the root of the source
+ *  tree. All contributing project authors may be found in the AUTHORS
+ *  file in the root of the source tree.
+ *
+ *  Based on code from the OggTheora software codec source code,
+ *  Copyright (C) 2002-2010 The Xiph.Org Foundation and contributors.
+ */
+#if !defined(_y4minput_H)
+# define _y4minput_H (1)
+# include <stdio.h>
+# include "vpx/vpx_image.h"
+
+
+
+typedef struct y4m_input y4m_input;
+
+
+
+/*The function used to perform chroma conversion.*/
+typedef void (*y4m_convert_func)(y4m_input *_y4m,
+ unsigned char *_dst,unsigned char *_src);
+
+
+
+struct y4m_input{
+  int               pic_w;
+  int               pic_h;
+  int               fps_n;
+  int               fps_d;
+  int               par_n;
+  int               par_d;
+  char              interlace;
+  int               src_c_dec_h;
+  int               src_c_dec_v;
+  int               dst_c_dec_h;
+  int               dst_c_dec_v;
+  char              chroma_type[16];
+  /*The size of each converted frame buffer.*/
+  size_t            dst_buf_sz;
+  /*The amount to read directly into the converted frame buffer.*/
+  size_t            dst_buf_read_sz;
+  /*The size of the auxilliary buffer.*/
+  size_t            aux_buf_sz;
+  /*The amount to read into the auxilliary buffer.*/
+  size_t            aux_buf_read_sz;
+  y4m_convert_func  convert;
+  unsigned char    *dst_buf;
+  unsigned char    *aux_buf;
+};
+
+int y4m_input_open(y4m_input *_y4m,FILE *_fin,char *_skip,int _nskip);
+void y4m_input_close(y4m_input *_y4m);
+int y4m_input_fetch_frame(y4m_input *_y4m,FILE *_fin,vpx_image_t *img);
+
+#endif