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1 // Copyright 2014 The Chromium Authors. All rights reserved. | 1 // Copyright 2014 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 // | 4 // |
5 // This file contains an implementation of an H264 Annex-B video stream parser. | 5 // This file contains an implementation of an H264 Annex-B video stream parser. |
6 | 6 |
7 #ifndef MEDIA_FILTERS_H264_BIT_READER_H_ | 7 #ifndef MEDIA_FILTERS_H264_BIT_READER_H_ |
8 #define MEDIA_FILTERS_H264_BIT_READER_H_ | 8 #define MEDIA_FILTERS_H264_BIT_READER_H_ |
9 | 9 |
| 10 #include <stdint.h> |
10 #include <sys/types.h> | 11 #include <sys/types.h> |
11 | 12 |
12 #include "base/basictypes.h" | 13 #include "base/macros.h" |
13 #include "media/base/media_export.h" | 14 #include "media/base/media_export.h" |
14 | 15 |
15 namespace media { | 16 namespace media { |
16 | 17 |
17 // A class to provide bit-granularity reading of H.264 streams. | 18 // A class to provide bit-granularity reading of H.264 streams. |
18 // This is not a generic bit reader class, as it takes into account | 19 // This is not a generic bit reader class, as it takes into account |
19 // H.264 stream-specific constraints, such as skipping emulation-prevention | 20 // H.264 stream-specific constraints, such as skipping emulation-prevention |
20 // bytes and stop bits. See spec for more details. | 21 // bytes and stop bits. See spec for more details. |
21 class MEDIA_EXPORT H264BitReader { | 22 class MEDIA_EXPORT H264BitReader { |
22 public: | 23 public: |
23 H264BitReader(); | 24 H264BitReader(); |
24 ~H264BitReader(); | 25 ~H264BitReader(); |
25 | 26 |
26 // Initialize the reader to start reading at |data|, |size| being size | 27 // Initialize the reader to start reading at |data|, |size| being size |
27 // of |data| in bytes. | 28 // of |data| in bytes. |
28 // Return false on insufficient size of stream.. | 29 // Return false on insufficient size of stream.. |
29 // TODO(posciak,fischman): consider replacing Initialize() with | 30 // TODO(posciak,fischman): consider replacing Initialize() with |
30 // heap-allocating and creating bit readers on demand instead. | 31 // heap-allocating and creating bit readers on demand instead. |
31 bool Initialize(const uint8* data, off_t size); | 32 bool Initialize(const uint8_t* data, off_t size); |
32 | 33 |
33 // Read |num_bits| next bits from stream and return in |*out|, first bit | 34 // Read |num_bits| next bits from stream and return in |*out|, first bit |
34 // from the stream starting at |num_bits| position in |*out|. | 35 // from the stream starting at |num_bits| position in |*out|. |
35 // |num_bits| may be 1-32, inclusive. | 36 // |num_bits| may be 1-32, inclusive. |
36 // Return false if the given number of bits cannot be read (not enough | 37 // Return false if the given number of bits cannot be read (not enough |
37 // bits in the stream), true otherwise. | 38 // bits in the stream), true otherwise. |
38 bool ReadBits(int num_bits, int* out); | 39 bool ReadBits(int num_bits, int* out); |
39 | 40 |
40 // Return the number of bits left in the stream. | 41 // Return the number of bits left in the stream. |
41 off_t NumBitsLeft(); | 42 off_t NumBitsLeft(); |
42 | 43 |
43 // See the definition of more_rbsp_data() in spec. | 44 // See the definition of more_rbsp_data() in spec. |
44 bool HasMoreRBSPData(); | 45 bool HasMoreRBSPData(); |
45 | 46 |
46 // Return the number of emulation prevention bytes already read. | 47 // Return the number of emulation prevention bytes already read. |
47 size_t NumEmulationPreventionBytesRead(); | 48 size_t NumEmulationPreventionBytesRead(); |
48 | 49 |
49 private: | 50 private: |
50 // Advance to the next byte, loading it into curr_byte_. | 51 // Advance to the next byte, loading it into curr_byte_. |
51 // Return false on end of stream. | 52 // Return false on end of stream. |
52 bool UpdateCurrByte(); | 53 bool UpdateCurrByte(); |
53 | 54 |
54 // Pointer to the next unread (not in curr_byte_) byte in the stream. | 55 // Pointer to the next unread (not in curr_byte_) byte in the stream. |
55 const uint8* data_; | 56 const uint8_t* data_; |
56 | 57 |
57 // Bytes left in the stream (without the curr_byte_). | 58 // Bytes left in the stream (without the curr_byte_). |
58 off_t bytes_left_; | 59 off_t bytes_left_; |
59 | 60 |
60 // Contents of the current byte; first unread bit starting at position | 61 // Contents of the current byte; first unread bit starting at position |
61 // 8 - num_remaining_bits_in_curr_byte_ from MSB. | 62 // 8 - num_remaining_bits_in_curr_byte_ from MSB. |
62 int curr_byte_; | 63 int curr_byte_; |
63 | 64 |
64 // Number of bits remaining in curr_byte_ | 65 // Number of bits remaining in curr_byte_ |
65 int num_remaining_bits_in_curr_byte_; | 66 int num_remaining_bits_in_curr_byte_; |
66 | 67 |
67 // Used in emulation prevention three byte detection (see spec). | 68 // Used in emulation prevention three byte detection (see spec). |
68 // Initially set to 0xffff to accept all initial two-byte sequences. | 69 // Initially set to 0xffff to accept all initial two-byte sequences. |
69 int prev_two_bytes_; | 70 int prev_two_bytes_; |
70 | 71 |
71 // Number of emulation preventation bytes (0x000003) we met. | 72 // Number of emulation preventation bytes (0x000003) we met. |
72 size_t emulation_prevention_bytes_; | 73 size_t emulation_prevention_bytes_; |
73 | 74 |
74 DISALLOW_COPY_AND_ASSIGN(H264BitReader); | 75 DISALLOW_COPY_AND_ASSIGN(H264BitReader); |
75 }; | 76 }; |
76 | 77 |
77 } // namespace media | 78 } // namespace media |
78 | 79 |
79 #endif // MEDIA_FILTERS_H264_BIT_READER_H_ | 80 #endif // MEDIA_FILTERS_H264_BIT_READER_H_ |
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