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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 | |
3 // found in the LICENSE file. | |
4 // | |
5 // This file contains an implementation of a H264BitstreamBuffer class for | |
6 // constructing raw bitstream buffers containing NAL units in | |
7 // H.264 Annex-B stream format. | |
8 // See H.264 spec Annex B and chapter 7for more details. | |
9 | |
10 #ifndef MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_ | |
11 #define MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_ | |
12 | |
13 #include "base/gtest_prod_util.h" | |
14 #include "base/numerics/safe_conversions.h" | |
15 #include "media/base/media_export.h" | |
16 #include "media/base/video_frame.h" | |
17 #include "media/filters/h264_parser.h" | |
18 | |
19 namespace media { | |
20 | |
21 // Holds one or more NALUs as a raw bitstream buffer in H.264 Annex-B format. | |
22 // Note that this class currently does NOT insert emulation prevention | |
23 // three-byte sequences (spec 7.3.1). | |
24 class MEDIA_EXPORT H264BitstreamBuffer { | |
25 public: | |
26 H264BitstreamBuffer(); | |
27 ~H264BitstreamBuffer(); | |
28 | |
29 // Discard all data and reset the buffer for reuse. | |
30 void Reset(); | |
31 | |
32 // Append |num_bits| bits to the stream from |val|. | |
33 // |val| is interpreted in the host endianness. | |
34 template <typename T> | |
35 void AppendBits(size_t num_bits, T val) { | |
36 AppendU64(num_bits, static_cast<uint64>(val)); | |
37 } | |
38 | |
39 void AppendBits(size_t num_bits, bool val) { | |
40 DCHECK_EQ(num_bits, 1ul); | |
41 AppendBool(val); | |
42 } | |
43 | |
44 // Append a one-bit bool/flag value |val| to the stream. | |
45 void AppendBool(bool val); | |
46 | |
47 // Append a signed value in |val| in Exp-Golomb code. | |
48 void AppendSE(int val); | |
49 | |
50 // Append an unsigned value in |val| in Exp-Golomb code. | |
51 void AppendUE(unsigned int val); | |
52 | |
53 // Start a new NALU of type |nalu_type| and with given |nal_ref_idc| | |
54 // (see spec). Note, that until FinishNALU() is called, some of the bits | |
55 // may not be flushed into the buffer and the data will not be correctly | |
56 // aligned with trailing bits. | |
57 void BeginNALU(H264NALU::Type nalu_type, int nal_ref_idc); | |
58 | |
59 // Finish current NALU. This will flush any cached bits and correctly align | |
60 // the buffer with RBSP trailing bits. This MUST be called for the stream | |
61 // returned by data() to be correct. | |
62 void FinishNALU(); | |
63 | |
64 // Return number of full bytes in the stream. Note that FinishNALU() has to | |
65 // be called to flush cached bits, or the return value will not include them. | |
66 size_t BytesInBuffer(); | |
67 | |
68 // Return a pointer to the stream. FinishNALU() must be called before | |
69 // accessing the stream, otherwise some bits may still be cached and not | |
70 // in the buffer. | |
71 uint8* data(); | |
72 | |
73 private: | |
74 FRIEND_TEST_ALL_PREFIXES(H264BitstreamBufferAppendBitsTest, | |
75 AppendAndVerifyBits); | |
76 | |
77 // Allocate additional memory (kGrowBytes bytes) for the buffer. | |
78 void Grow(); | |
79 | |
80 // Append |num_bits| bits from U64 value |val| (in host endianness). | |
81 void AppendU64(size_t num_bits, uint64 val); | |
82 | |
83 // Flush any cached bits in the reg with byte granularity, i.e. enough | |
84 // bytes to flush all pending bits, but not more. | |
85 void FlushReg(); | |
86 | |
87 typedef uint64 RegType; | |
88 enum { | |
89 // Sizes of reg_. | |
90 kRegByteSize = sizeof(RegType), | |
91 kRegBitSize = kRegByteSize * 8, | |
92 // Amount of bytes to grow the buffer by when we run out of | |
93 // previously-allocated memory for it. | |
94 kGrowBytes = 4096, | |
95 }; | |
96 | |
97 COMPILE_ASSERT(kGrowBytes >= kRegByteSize, | |
98 kGrowBytes_must_be_larger_than_kRegByteSize); | |
99 | |
100 // Unused bits left in reg_. | |
101 size_t bits_left_in_reg_; | |
102 | |
103 // Cache for appended bits. Bits are flushed to data_ with kRegByteSize | |
104 // granularity, i.e. when reg_ becomes full, or when an explicit FlushReg() | |
105 // is called. | |
106 RegType reg_; | |
107 | |
108 // Current capacity of data_, in bytes. | |
109 size_t capacity_; | |
110 | |
111 // Current byte offset in data_ (points to the start of unwritten bits). | |
112 size_t pos_; | |
113 | |
114 // Buffer for stream data. | |
115 uint8* data_; | |
116 }; | |
117 | |
118 } // namespace media | |
119 | |
120 #endif // MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_ | |
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