media/filters/h264_bitstream_buffer.h

   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   static_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_