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
19namespace 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).
24class 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_
121