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_ 121