Add HE AAC support to ISO BMFF.

media/base/bit_reader.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_BIT_READER_H_
+#define MEDIA_BASE_BIT_READER_H_
+
+#include <sys/types.h>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// A class to read bit streams.
+class MEDIA_EXPORT BitReader {
+ public:
+  // Initialize the reader to start reading at |data|, |size| being size
+  // of |data| in bytes.
+  BitReader(const uint8* data, off_t size);
+  ~BitReader();
+
+  // Read |num_bits| next bits from stream and return in |*out|, first bit
+  // from the stream starting at |num_bits| position in |*out|.
+  // |num_bits| cannot be larger than the bits the type can hold.
+  // Return false if the given number of bits cannot be read (not enough
+  // bits in the stream), true otherwise. When return false, the stream will
+  // enter a state where further ReadBits/SkipBits operations will always
+  // return false unless |num_bits| is 0. The type |T| has to be a primitive
+  // integer type.
+  template<typename T>
+  bool ReadBits(int num_bits, T *out) {
+    DCHECK_LE(num_bits, static_cast<int>(sizeof(T) * 8));

[Ami GONE FROM CHROMIUM, 2012/07/19 00:28:59]

For being in the header there's a lot of space taken for what can be just:
DCHECK_LE(num_bits, static_cast<int>(sizeof(T) * 8));
uint64 temp;
bool ret = ReadBitsInternal(num_bits, &temp);
*out = static_cast<T>(temp);
return ret;

[xiaomings, 2012/07/19 01:11:02]

Done.

+
+    uint64 temp;
+
+    if (ReadBitsInternal(num_bits, &temp)) {
+      *out = static_cast<T>(temp);
+
+      return true;
+    }
+
+    *out = 0;
+    return false;
+  }
+
+ private:
+  // Help function used by ReadBits to avoid inlining the bit reading logic.
+  bool ReadBitsInternal(int num_bits, uint64* out);
+
+  // Advance to the next byte, loading it into curr_byte_.
+  // If the num_remaining_bits_in_curr_byte_ is 0 after this function returns,
+  // the stream has reached the end.
+  void UpdateCurrByte();
+
+  // Pointer to the next unread (not in curr_byte_) byte in the stream.
+  const uint8* data_;
+
+  // Bytes left in the stream (without the curr_byte_).
+  off_t bytes_left_;
+
+  // Contents of the current byte; first unread bit starting at position
+  // 8 - num_remaining_bits_in_curr_byte_ from MSB.
+  uint8 curr_byte_;
+
+  // Number of bits remaining in curr_byte_
+  int num_remaining_bits_in_curr_byte_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BitReader);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_BIT_READER_H_