| // Copyright 2014 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. |
| // |
| // 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 "base/macros.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(); |
| |
| // 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 1-32, 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_; |
| |
| DISALLOW_COPY_AND_ASSIGN(H264BitReader); |
| }; |
| |
| } // namespace media |
| |
| #endif // MEDIA_VIDEO_H264_BIT_READER_H_ |