Add vp9 QP parser.

webrtc/modules/video_coding/utility/vp9_uncompressed_header_parser.h

+/*
+ *  Copyright (c) 2017 The WebRTC 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.
+ */
+
+#ifndef WEBRTC_MODULES_VIDEO_CODING_UTILITY_VP9_UNCOMPRESSED_HEADER_PARSER_H_
+#define WEBRTC_MODULES_VIDEO_CODING_UTILITY_VP9_UNCOMPRESSED_HEADER_PARSER_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "webrtc/base/bitbuffer.h"
+#include "webrtc/base/logging.h"
+
+namespace webrtc {
+
+namespace vp9 {
+
+class VP9BitReader : public ::rtc::BitBuffer {
+ public:
+  VP9BitReader(const uint8_t* buffer, size_t length_)
+      : BitBuffer(buffer, length_) {}
+
+  uint32_t GetBit() {
+    uint32_t bit = 0;
+    if (ReadBits(&bit, 1))
+      return bit;
+
+    LOG(LS_WARNING) << "Failed to get QP. Reached EOF.";

[brandtr, 2017/05/23 08:59:02]

Since this is a general bit reader, maybe make the error message more general?
Something like "Failed to get bit. Reached EOF."?

[jianj1, 2017/05/23 17:37:30]

Done.

+    return 0;
+  }
+
+  uint32_t GetValue(int bits) {
+    uint32_t value = 0;
+    if (ReadBits(&value, bits))
+      return value;
+
+    LOG(LS_WARNING) << "Failed to get QP. Reached EOF.";

[brandtr, 2017/05/23 08:59:02]

And here.

[jianj1, 2017/05/23 17:37:30]

Done.

+    return 0;
+  }
+
+  int32_t GetSignedValue(int bits) {
+    const int32_t value = static_cast<int>(GetValue(bits));
+    return GetBit() ? -value : value;
+  }
+};
+
+// Gets the QP, QP range: [0, 255].
+// Returns true on success, false otherwise.
+bool GetQp(const uint8_t* buf, size_t length, int *qp);

[brandtr, 2017/05/23 08:59:02]

int* qp

[jianj1, 2017/05/23 17:37:30]

Done.

+
+}  // namespace vp9
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_UTILITY_VP9_UNCOMPRESSED_HEADER_PARSER_H_