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// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// This file contains an implementation of an H264 Annex-B video stream parser.
#ifndef MEDIA_VIDEO_H264_BIT_READER_H_
#define MEDIA_VIDEO_H264_BIT_READER_H_
#include <stddef.h>
#include <stdint.h>
#include <sys/types.h>
#include "media/base/media_export.h"
namespace media {
// A class to provide bit-granularity reading of H.264 streams.
// This is not a generic bit reader class, as it takes into account
// H.264 stream-specific constraints, such as skipping emulation-prevention
// bytes and stop bits. See spec for more details.
class MEDIA_EXPORT H264BitReader {
public:
H264BitReader();
H264BitReader(const H264BitReader&) = delete;
H264BitReader& operator=(const H264BitReader&) = delete;
~H264BitReader();
// Initialize the reader to start reading at |data|, |size| being size
// of |data| in bytes.
// Return false on insufficient size of stream..
// TODO(posciak,fischman): consider replacing Initialize() with
// heap-allocating and creating bit readers on demand instead.
bool Initialize(const uint8_t* data, off_t size);
// 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| may be 1-31, inclusive.
// Return false if the given number of bits cannot be read (not enough
// bits in the stream), true otherwise.
bool ReadBits(int num_bits, int* out);
// Return the number of bits left in the stream.
off_t NumBitsLeft();
// See the definition of more_rbsp_data() in spec.
bool HasMoreRBSPData();
// Return the number of emulation prevention bytes already read.
size_t NumEmulationPreventionBytesRead();
private:
// Advance to the next byte, loading it into curr_byte_.
// Return false on end of stream.
bool UpdateCurrByte();
// Pointer to the next unread (not in curr_byte_) byte in the stream.
const uint8_t* 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.
int curr_byte_;
// Number of bits remaining in curr_byte_
int num_remaining_bits_in_curr_byte_;
// Used in emulation prevention three byte detection (see spec).
// Initially set to 0xffff to accept all initial two-byte sequences.
int prev_two_bytes_;
// Number of emulation preventation bytes (0x000003) we met.
size_t emulation_prevention_bytes_;
};
} // namespace media
#endif // MEDIA_VIDEO_H264_BIT_READER_H_