Adding video reader/writer APIs.

Right now only IVF format is supported which is enough for example code.
Other formats like y4m, webm, raw yuv will be supported later.

Change-Id: I34c6f20731c1851947587ca5c589d7856b675164

video_reader.c

diff --git a/video_reader.c b/video_reader.c
new file mode 100644
index 0000000..4be7483
--- /dev/null
+++ b/video_reader.c
@@ -0,0 +1,81 @@
+/*
+ *  Copyright (c) 2014 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "./ivfdec.h"
+#include "./video_reader.h"
+
+static const char *const kIVFSignature = "DKIF";
+
+struct VpxVideoReaderStruct {
+  VpxVideoInfo info;
+  FILE *file;
+  uint8_t *buffer;
+  size_t buffer_size;
+  size_t frame_size;
+};
+
+VpxVideoReader *vpx_video_reader_open(const char *filename) {
+  char header[32];
+  VpxVideoReader *reader = NULL;
+  FILE *const file = fopen(filename, "rb");
+  if (!file)
+    return NULL;  // Can't open file
+
+  if (fread(header, 1, 32, file) != 32)
+    return NULL;  // Can't read file header
+
+  if (memcmp(kIVFSignature, header, 4) != 0)
+    return NULL;  // Wrong IVF signature
+
+  if (mem_get_le16(header + 4) != 0)
+    return NULL;  // Wrong IVF version
+
+  reader = calloc(1, sizeof(*reader));
+  if (!reader)
+    return NULL;  // Can't allocate VpxVideoReader
+
+  reader->file = file;
+  reader->info.codec_fourcc = mem_get_le32(header + 8);
+  reader->info.frame_width = mem_get_le16(header + 12);
+  reader->info.frame_height = mem_get_le16(header + 14);
+  reader->info.time_base.numerator = mem_get_le32(header + 16);
+  reader->info.time_base.denominator = mem_get_le32(header + 20);
+
+  return reader;
+}
+
+void vpx_video_reader_close(VpxVideoReader *reader) {
+  if (reader) {
+    fclose(reader->file);
+    free(reader->buffer);
+    free(reader);
+  }
+}
+
+int vpx_video_reader_read_frame(VpxVideoReader *reader) {
+  return !ivf_read_frame(reader->file, &reader->buffer, &reader->frame_size,
+                         &reader->buffer_size);
+}
+
+const uint8_t *vpx_video_reader_get_frame(VpxVideoReader *reader,
+                                          size_t *size) {
+  if (size)
+    *size = reader->frame_size;
+
+  return reader->buffer;
+}
+
+const VpxVideoInfo *vpx_video_reader_get_info(VpxVideoReader *reader) {
+  return &reader->info;
+}
+