103 lines
3.2 KiB
C++
103 lines
3.2 KiB
C++
// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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//
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// This file contains an implementation of an H264 Annex-B video stream parser.
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#ifndef PACKAGER_MEDIA_CODECS_H264_BIT_READER_H_
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#define PACKAGER_MEDIA_CODECS_H264_BIT_READER_H_
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#include <sys/types.h>
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#include <cstdint>
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#include <packager/macros.h>
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namespace shaka {
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namespace media {
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// A class to provide bit-granularity reading of H.264/H.265 streams.
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// This is not a generic bit reader class, as it takes into account
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// H.264 stream-specific constraints, such as skipping emulation-prevention
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// bytes and stop bits. See spec for more details.
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class H26xBitReader {
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public:
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H26xBitReader();
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~H26xBitReader();
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// Initialize the reader to start reading at |data|, |size| being size
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// of |data| in bytes.
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// Return false on insufficient size of stream..
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bool Initialize(const uint8_t* data, off_t size);
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// Read |num_bits| next bits from stream and return in |*out|, first bit
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// from the stream starting at |num_bits| position in |*out|.
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// |num_bits| may be 1-32, inclusive.
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// Return false if the given number of bits cannot be read (not enough
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// bits in the stream), true otherwise.
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bool ReadBits(int num_bits, int* out);
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// Read a single bit and return in |*out|.
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// Return false if the bit cannot be read (not enough bits in the stream),
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// true otherwise.
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bool ReadBool(bool* out) {
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int value;
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if (!ReadBits(1, &value))
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return false;
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*out = (value != 0);
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return true;
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}
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// Skips the given number of bits (does not have to be less than 32 bits).
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// Return false if there aren't enough bits in the stream, true otherwise.
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bool SkipBits(int num_bits);
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// Exp-Golomb code parsing as specified in chapter 9.1 of the spec.
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// Read one unsigned exp-Golomb code from the stream and return in |*val|.
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bool ReadUE(int* val);
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// Read one signed exp-Golomb code from the stream and return in |*val|.
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bool ReadSE(int* val);
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// Return the number of bits left in the stream.
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off_t NumBitsLeft();
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// See the definition of more_rbsp_data() in spec.
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bool HasMoreRBSPData();
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// Return the number of emulation prevention bytes already read.
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size_t NumEmulationPreventionBytesRead();
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private:
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// Advance to the next byte, loading it into curr_byte_.
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// Return false on end of stream.
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bool UpdateCurrByte();
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// Pointer to the next unread (not in curr_byte_) byte in the stream.
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const uint8_t* data_;
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// Bytes left in the stream (without the curr_byte_).
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off_t bytes_left_;
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// Contents of the current byte; first unread bit starting at position
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// 8 - num_remaining_bits_in_curr_byte_ from MSB.
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int curr_byte_;
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// Number of bits remaining in curr_byte_
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int num_remaining_bits_in_curr_byte_;
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// Used in emulation prevention three byte detection (see spec).
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// Initially set to 0xffff to accept all initial two-byte sequences.
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int prev_two_bytes_;
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// Number of emulation preventation bytes (0x000003) we met.
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size_t emulation_prevention_bytes_;
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DISALLOW_COPY_AND_ASSIGN(H26xBitReader);
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};
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} // namespace media
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} // namespace shaka
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#endif // PACKAGER_MEDIA_CODECS_H264_BIT_READER_H_
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